u/never_before19

So i got my period 5 days ago and simultaneously started birth control because of ovulation, period and pre period pain. I try to take my pill at 19.30 everyday however i noticed today that from 16 till 19.30 my uterus was aching. after i took my pill the pain went away. could this already be a side effect? is this normal ? my period blood usually fully stops at day 5 but now ive bern having way more brown blood at the end (this is know is normal).

update: i still have very bad uterus pain