i was on minocycline back in the day and it worked really good for me and totally cleared me up and then i was put on amoxicillin a few years after that which did nothing! 5 years ago when i was breaking out again the derm decided to give me bactrim which gave me an allergic reaction and then a few years later i was put on doxcycyline. i took that on and off at higher and lower doses for 2 years and then it stopped working and then i was given zithromax which did nothing and then last year keflex which cleared me in 5 days. i am weaning off it now but i think each time you use antibiotics you need to go to the next stronger one for them to work. my acne is totally hormonal so i am on spiro as well but for some reason antibiotics work so well for me in that they totally stop all my acne completely.
a girl i work with was on minocycyline for 8 years and got off it two years ago with no problems and a lady at the derm's office was on them for 2 years with no issues at all so it just depends on the person. also low dose doxcycline which would be 50mg a day is fine to take forever because it doesnt disturb gut flora and is totally safe so that is an option as well. sometimes you just need to experiment with different antibiotics because some of them work and some dont.
i would recommend that you have a good skincare regimen too because that will help a lot especially for when you do eventually decide to stop the antibiotics.