It could be implantation bleeding, or if your using endometrium, I had bleeding on and off til I was 12 weeks some was actually gushes I am currently 27+3 (Ivf 5 day blast) with twins girls it's a very long road don't stress relax good luck!!!!
best of luck to you! I don't have any personal experience with IVF yet but I have definitely said a prayer for you. I hope you hear wonderful news Monday!