Hi thanks for your question.
The irregular bleeding is called as menorrhagia
and there are many causes for menorrhagia.Uterine fibroids and endometrosis are the common one.It could be by chance that your bleeding started after sex.or it could be possible that you bleeding had decreased and sex aggrevated it.You need ultrasound
abdomen to know the cause of your menorrhagia.I would suggest you to consult a gynaecologist may be able to evaluate you for menorrhagia.
Hope this answers your question.