What Causes Stomach Pain And Headaches?

hi im female and 18 years of age. last year i was getting really bad pains in my stomach on the right side above my ovaries i was worried so went to the health clinic and everything was fine. the pain has come back again a few months ago so i went to the doctors they did a check up on my ovaries for any cysits etc.. the resalts were fine. the pain was horrible i couldnt have sex with oout it hurting or even use a tampon. the pain has gone nowbut i have been getting over pain in my stomach and it feels ike all my muscles ach, my periods are still all over the place, ive been putting alot of weight on recently which i dont under stand as im not eating much and go on walks every day. i also been getting bad headahes, lack of seep which leads to tierdness and also alot of stress i feel down alot of the time. do you have any answers for me please