21 year old female constanly fatigued?

I'm a 21 year old female relatively good health I exercise at least 5 times a week moderately to mild I'm only 118 pounds I have had bloodwork and my doctor said my thyroid was off afew points.. sent me in for an ultrasound and said it looked fine I have a history of ovarian cysts and have recently been to my gyno they only seem interested in making a buck off surgery....the guy literally mentioned surgery before even giving me an exam LOL! come on now. he said possible endometriosis because I explained having pain during intercourse at times and an episode of terrible pain in my pelvic area a couple times but subsided with Tylenol and a heating pad papsmears were normal I have given birth before and it took only 4 months for me to get pregnant I explained that it was probably not endo but you know doctors I'm sure I also know im not anemic but have been in the past does anyone know why I could possibly be this fatigued constantly??