I'm 21 years old and I had taken Minocycline for a while and heard if u take it too long u get grey spots and stuff so my skin was clear and I decided to come off it but then I got some pimples around my chin and didn't like it so I went to the derm and asked if I could try doxycycline (cause my brother takes it) and I took it for about 2 weeks and it broke me out so bad I was so upset! I had deep pimples that I couldn't cover up. I called my derm and said it didn't work for me and did the opposite so she gave me some more Minocycline again, I've been on it for almost 2 weeks and I still have some big pimples on my cheek. I'm so self conscious and so embarrassed to leave my house. If anyone has some advice or anything I'd greatly appreciate it because this is making me really upset 
Use the minocycline exactly the way your doctor tellsyou. I used minocycline at full dose foryears, it's very safe and I never turned gray. I sorry, but it's benefits don't always happen quickly. If it worked once already then it will probably work again.
If you are not usingtopical treatments, you should start immediately. Benzoyl peroxide wash or lotion will supplement the antibiotics, and prevent resistance. Retinoids clear your pores and prevent white/black heads from ever appearing.
You can eventually come off antibiotics but I don't recommend tapering every other day.You can take a full doseuntil the deep cysts go away and reduce the dose. Take the half dose untilthe inflammatory acne (red spots) mostly goes away.
I think that antibiotics should be used no more than a year. After that, ifyou can't control your acne with topicals alone. You should take accutane.
Thats my opinion