Had sex yesterday at 8am (bf came inside) on tricyclen, (10th pill day). i am bleeding thin blood unlike menstrual fluid w.o odor. pregnant? cause?

Not pregnant: It is too soon to show any signs of pregnancy, and unlikely with oral contraceptives taken correctly. This is some form of break-through-bleeding, but its cause is indeterminate.

Possible but...: Any time you have irregular bleeding, you should do a pregnancy test. Having said that, what you did yesterday won't show up today. It would be positive from a previous act. Also, it may be that your bcp's need adjusting. I'd recommend doing a pregnancy test and then calling your doctor as he/she knows your history.