Skipping Periods

Cat

It’s been 138 days (almost 5 months) since my last period but I know for a fact I’m not pregnant. My male Doctor didn’t seem concerned whenever I told him and would just say that it’s natural to be irregular cause I’m young (19) I’ve been getting them since I was 12. Should I be worried. (My concern is that my doctor is sexist and will refuse to see me if I have makeup on because it shows I’m not really sick.)