I have read your question,
Just using anti-biotics is not sufficient to cure the bruising , along with it I recommend you to use systemic anti-inflammatory drugs and apply Anti-thrombolytic ointment on the affected area for better relief.
The blood clot on the affect area may be the cause of bruising , sitting on a hard surface may cause the reappearance of bruising .
I suggest you to not sit on hard surfaces until the bruising and pain subside.
Further I also suggest you to consult a physician nearby for further medical advice
Wishing you a good health,