Why is my scalp itchy, flaky, and red?

I’ve been having problems with my scalp for about… almost 5 months now Around my hairline a little past that now my scalp is itchy flaky & red it seems like the more I scratch (I always use a comb) the darker it gets where I scratch at first I thought it was just simple dandruff because I’ve had dandruff problems before in the past I kept using my dandruff shampoo (selsun blue moisturizing mediated its green that’s always worked for me) & I’m like “Hmmm? doesn’t seem to be getting any better maybe I should find a new dandruff shampoo” I went to go pick up a stronger one its Neutrogena for dandruff & scalp build up with silic acid (sp?) The bottle is almost gone now & that didn’t help either

so I’ve been goggling to see what other people have done I’ve changed my shampoos & conditioners that didn’t help I’ve even used homemade remedies like vinegar water, green tea & a few others that didn’t help

I recently came across Scalp psoriasis, Psoriasis & Seborrheic dermatitis I’ve been looking at pictures & reading about the symptoms It looks about the same as what’s going on with my scalp but I’m not sure I’ve also noticed a few months ago that I had this weird dry patch on my elbow It looked like a patch of skin on my elbow had been grated & dried it was really rough & hurt I tried putting oils on it, exfoliating it, & nothing seemed to help I just noticed recently that it’s calmed down & smaller I’m not sure what helped with that I’m not sure if the two are linked or not

Sorry this question is so long but I don’t want to leave out any info I really need help! I don’t know what to do or what it could be…. Thanks!