Benzoyl peroxide stopped working for my acne so my doctor added doxycycline 100mg to my regimen. Is this enough or should I replace benzoyl peroxide?

You decide. You can continue using the benzoyl peroxide if you tolerated it and it once was sufficient. I was able to stop using acne medications at age 50. The tretinoin is also your choice. It's worth the effort. The dose of 100 mg 1-2x/day for Doxycycline is a reasonable one. Good luck.