Hello, and thank you for your question. I will be happy to assist you. Answers are for educational purposes only.
I am not familiar with sachets therapy....what is it?
If you took antibiotics for the cystitis, that can cause a simple vaginal infection such as yeast or bacterial vaginosis which could account for your discharge/bleeding.
Alternatively, having a recent illness such as cystitis can cause an irregularity to your cycle resulting in some unexpected bleeding.
Let me know what you took and I will be happy to explore this with you further.