Energy Help

I'm an 18 year old male and I ship off to marine corp boot camp in 2 months so for the past 6-7 months i'v been working out at least 3 times a week. I'm going through cycles where my muscles get fatigued really easily. I have no energy to have a workout. I'll be in perfect shape, then suddenly for the next month my muscles can't handle as much as they could. I eat nothing but good portions of healthy food, drink nothing but water, get 10 hours of sleep every night, and I stretch well before every work out. I'm very serious about my work out schedule so I give my body plenty of rest and don't over-work myself. I get good sleep every night but I never feel refreshed when I wake up. I don't understand what is causing my lack of energy and i've already talked to a nurse about it and they even were stumped. If anyone knows what could be wrong it would be greatly appreciated.