Hello Dr. I am taking doxycycline now day 7 and my face is broke out into an itchy rash. I too 10 ml of childrens byenadryl because that is all I have?

Benadryl (diphenhydramine) 10 ml of oral solution is 25 mg, you can double that if no improvement, i.e. 50 mg/dose, if reaction is more severe go to ER or call 911. Stop the doxycycline, and call your doctor/prescriber, best wishes.