Blood clot in uterus. Ghis antibiotics?

I am in fertility treatment. Last month My doctor prescribed me letrouz 2.5 day 1 to day 10. Corectia twice daily and trafolic tab daily. Day 16 to 26 sustwn sr 300. Last cycle I have gone through follicular study and one follicle ruptured. There were some fluids in POD. In this cycle my Lmp date 23th March. To day is day 9 same medication I have started. Yesterday again I follicular scan has done. In my report I have total three follicle in LO and RO. But a small blood clots has seen in uterus. ET is 4.3mm. Dr. Stopped letrouz yesterday. For that clot she prescribed me Cynomicyn 100 for 10 days. As I am trying for concieving can take ghis antibiotics? Why this clot in this cycle as it was not there in my previous cycle. Please guide me..