period on birth control

ok ladies-

I started taking the pill after I had a still born in may. I had no issues until November when my pharmacy sent me a different generic version.

I started on my third week of pills and had a 10 period and ended near the end of week 4 pills.

Ever since I've started on week three or as early as week 2, having heavy periods that last over 10 days. This month I had a period in week 2 and it stopped for a few days and started again in the middle of week 4.

I've talked to my OB and nothing came of it. I've started to become exhausted before/during/after cycle days, terrible cramping, and just feel awful.

any ideas on why this is happening?