Spiro stopped working? Did I become immune?

I've been on Spironolactone & Minocycline (100mg daily) since 2012 and had clear skin since then. I went off for a while when I was without insurance. Now I'm back on both & they worked great for about a year but over the last few months it seems like they've stopped working. I'm taking em, but my cystic acne is back bad. My derm suggested that we up the Spyro to 200mg a day but I really fear an IB. Did I become immune? Will I experience an IB by upping the dosage? Will this even work? Thanks!