Was on my period for 3weeks, now on the bc to stop the bleeding. i've been on the birth control for 4 days im still spotting. is it anything to worry?

No : It can take a few cycles for your body to adjust to birth control.

Breakthrough bleed: I wouldn't be too concerned. Most bc pills on the market are lower dose and as a result you may have some breakthrough bleeding on the first couple of cycle packs. While its a pain to have the bleeding, the side effects of high dose birth control can be worse. Personally i give Provera (medroxyprogesterone) or another Progesterone to shed the lining before starting to pill to prevent this bleeding issue.