I Get Sores On My Scalp And Started Taking Tetralysal

I get sores on my scalp and started taking Tetralysal about 3 years ago. It cleared my scalp with 2 weeks and I have been taking it ever since. In between I stopped taking it for a few months and all was clear. The. When it started I repeated the procedure. The last 3 months my scalp has not cleared. It seems like the medication has stopped working. Any advise?