Thanks for the query to H.C.M. Forum.
Irritation started in uterus , so may be due to contraception
drugs as you indicated yourself.
This type of bleeding sometimes heavy other times light , we call as irregular bleeding.
Irregular bleeding with pain on the right lower abdominal site may be due to .
1 Poly Cystic Ovarian Disease
( pcod) as this is very common disease in this age group with these symptoms.
2 The 2nd possibility may be due to appendix , as you are complaining that there is pain in lower right abdomen with nausea
, so may be due to appendix infection
. Diagnosis can be confirmed by ultrasound
In my opinion consult a gynecologist and get his opinion for pcod .