Originally Posted by TMonk

@StodaD do you train with power? Do you know what your w/kg is? Body weight? If it makes you fatigued to move up in a cat 3 crit, you need more fitness and/or skill. Riding on the very back of the race should be easier than the middle as you can "tailgun" by leaving a gap and taking corners faster. Practice moving up using a minimum of energy. Be patient.

Another solution is to attack! If it makes you nervous to be in the pack, go of the front. But really I think you just need to be patient and do it more. It's OK if it takes you a few races (or a whole season) to find your groove.