Hi prettybutterfly,
The bleeding could be form ovulation (?) Have you ever had this sort of bleeding before? It is also very very likely that the bleeding is from DTD. Doxycycline is not safe in pregnancy (will discolour bub's teeth & bones). It is unlikely to affect you this early (ie. if you DTD on monday then there is no implantation yet to cause problems to the embie.). Can you stop the antibiotics until you find out for sure? I'm assuming you're on it long term for skin condition - try using something topical like clearasil for now. HTH and maybe speak to your Dr or pharmacist for more advise.