Irritating scalp when using Minoxidil, how to fix it?

29 year old male had my 2nd transplant in Nov 2015, my 1st transplant was in Nov 2013. After my 1st transplant, I started using Minoxidil 5% and was all good, the scalp was fine and it was good until but after 6 months it started irritating the scalp and caused a thick white coat on the scalp resulting in hair loss. I immediately stopped Rogaine used Nizoral to treat it. I miss using Rogaine, tried Rogaine foam same result, any idea how i can start using minoxidil without hurting the scalp?