I have read that doxycycline can delay your period. Are there any signs of pregnancy I should be looking for?

A positive test . Don't guess. Take a test. In today's world you do not need to wonder if you are pregnant or not based on symptoms. Pregnancy tests are available at any pharmacy and in minutes you will have your answer. They can detect a pregnancy 7-10 days after conception. The best time to take one is when you miss your period.