Just keep riding. It'll come. Find a compatible group and ride with them once a week, or a few times a month. That made a huge difference in my enjoyment of cycling and fitness. I was in terrible shape when I resumed cycling in 2015 after 30+ years away, and in my late 50s. Getting dropped on every hill motivated me to keep chugging and plugging away. Took awhile but I got stronger and faster. You're young so it'll come quicker for you. Took me over a year to see much progress.
I don't have a rigid schedule for training, but I try to do an interval session once a week (15-30 minutes), a couple of moderate effort long rides (50-60 miles), and one harder effort semi-longish ride (20-30 miles without stops). Works for me. Younger folks could ride more often, farther and faster. I have to be realistic about my age and recovery time.
Regarding cramps... nobody knows. Seriously, even researchers don't know.
Some folks are more prone than others to muscle cramps. I've had painful muscle spasms on and off my whole life. Got 'em so bad after a 60+ mile ride Sunday I literally fell on the floor rolling around hollering and laughing because the spasms kept jumping from one part of my body to another. Started with the thigh, then as soon as I tried to sort that out it hit my abdominal muscles, then my calves, then the arches of my feet. By the time it was finished I had a bruise on my shoulder blade from rolling on the floor.
Multiple world boxing champ Manny Pacquiao has been plagued with muscle spasms, mostly in his legs. He makes a gazillion dollars and can afford the best possible medical treatment. If there was a surefire cure he'd have found it. But nobody knows for certain what causes it or how to fix it.
I also use a roller on the muscles I can reach -- a heavy marble rolling pin. It works. Makes good biscuits too.
Some folks swear by electrolytes and supplements. Some swear at it and say it's hogwash. But it works for me.
Best rescue electrolyte I've tried is DropDrop ORS. Comes in single serving Mylar packets. It's pricey but it works. Not only has it saved my bacon, it's worked on friends who've suffered muscle cramps or sudden onset of heat exhaustion. I didn't hard-sell it to them. I just put some in their water bottles, told 'em to drink the whole thing and wait about 15 minutes. Did the trick. There are lots of electrolytes around and they all do pretty much the same thing, but DripDrop has research to back up their claims (see their website). But the trick is to mix it appropriately -- not too dilute or concentrated. It needs the right amount of sugar to be absorbed quickly.
I carry a couple of the Mylar packets in my saddle bag or jersey pockets, every ride. And I've shared 'em a couple of times. It works. I'd imagine NUUN and others work as well, but the single serve Mylar packets are handy and waterproof, and take up practically no room even in my smallest saddle bag.
Some folks swear by pickle juice. I was skeptical, figuring that salt is salt and it doesn't matter what form it's in. But some research indicates it may have nothing to do with electrolyte replacement -- which would take around 15 minutes to begin to help -- and may have more to do with effects on the vagus nerve, which could explain the nearly immediate relief some folks claim for pickle juice.
I also use all kinds of voodoo potions. I'll only say it seems to work for me.
Pre-ride, at least an hour or so before a hard workout or group ride, I'll drink a bottle with creatine and BCAAs, a bit of powdered veggie material that's supposedly high in ecdysterone, an anabolic agent that's -- for now -- not banned and seems to be effective. It's found in spinach and other greens, and even in some insects and shellfish.
I take magnesium lactate, which seems to be more effective than other common forms of magnesium -- citrate, glycinate, etc. It sure seems to work. And I understand why it's not used more often. Magnesium lactate causes ferocious intestinal gas. It's almost comical how much I fart from the stuff. But it sure seems to work. It's one of the ingredients in Sportlegs, a supplement some friends swear by for muscle cramps. Supposedly the lactate forms of magnesium and calcium provide what the muscles need, quicker.
I do notice quicker recovery from harder efforts. Before, with short, steep punchy sprint-climbs, I'd be gassed out and lagging behind, usually getting dropped on faster group rides. Now I recover much more quickly and can catch up. That's a pretty common claim for success stories using creatine and mag lactate.
And in the real voodoo category, I also take DHEA, pregnenolone and other stuff. It's all legal, you can buy it anywhere. Does it help? I dunno. I'm recovering from thyroid cancer and need synthetic thyroid supplements, have borderline anemia and other stuff. So I'll try anything that might help. I won't claim any miracles but it doesn't seem to hurt anything.