Hello,
Welcome to the ehealthforum and I am really glad to help you out. Your concern is regarding the irregularity in periods and the intermenstrual bleeding that you are having. Since you are having irregularity in menstrual cycles, so this can be due to two obvious causes in your case. It can be due to stress or anxiety or hormonal imbalance caused by the post coital pills. The symptoms are not suggestive of any pregnancy but to have peace of mind, you should get your serum HCG levels estimated which is a more accurate test than urine test for pregnancy.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care.