No client is going to appreciate blood on his mouth/cock. Unless it is light spotting, I wouldn't recommend going ahead with bookings unless you use a sponge or warn clients (I think many escorts offer a discount in this case).
How long have you been continously been taking the pill for? I use the contraceptive pill and I find that if I skip periods for long enough, I start getting heavy spotting (I can skip every other period, but no more).