One thing I do is lift weights at the gym, and that helps the speed and stamina, but if I don't go lift, I see a significant loss of speed and stamina.
That's too bad.
Your post makes you sounds like someone that feels very tired - so much so - that they they think taking certain pills will make you feel better. Worse yet, you seem to have other misunderstandings about the nature of exercise and fitness for a given task. (cycling namely)
In general most people use carbohydrate-rich snacks and food to maintain stamina during rides. How much speed a cyclist can produce is often defined by their personal power-to-weight ratio. Although, specific muscle strengthening exercise could help in certain situations.
Good luck with your current routines.