What Causes Pain In Uterus?

I''m a 25 year old female, i weight 211 and i'm 5'6. I have been having very sharp pains in the uterus area on the left side. i've been to see my doctor but all my test came back normal. the pain is very sharp to the point i can't stand straight and i have to sit down and i feel sick and tired afterwards. is it something to worry about or do i have to make an appointment to see my doctor again?