Hurts him??

Ok so when I give my man head I absolutely DO NOT use teeth or anything what so ever to hurt him and I'm really gentile but he says it gets uncomfortable and his top gets irritated? I use plenty of spit and everything and I just don't know what I'm doing wrong😞 like sometimes he will say it felt good like half the time and the rest was uncomfortable and I just can't seem to figure out what I need to do. Any tips? I