I have painful periods and very heavy bleeding. The dr. Put me on birth control, but we want another baby.?

Needs eval, pref REI. Need evaluation for polyps inside uterus, fibroids (depends on their size and location), endometriosis (tissue similar to the lining of the uterus gets outside uterus), adenomyosis which is endometriosis in uterine wall. See ob/gyn or reproductive endocrinologist (rei). Reis do ultrasound, saline sonohysterogram (shg) to check your uterus. Newer surgical techniques better than D&C or resectoscope.
Temporary. Using birth control pills for this problem is usually temporary. Once you want to become pregnant, come off the pills 2-3 months before you want to try and hopefully, by then, the cycles will not be as bad.