There is nothing even remotely unusual about your head shape. The skull is not a bowling ball and every skull has imperfections that will show up if you study it closely enough, so you are probably just finding those kinds of things. A forehead would look weird if it went straight up without a slope. For the record, I am not doing that dishonest supportive "oh your look fine" crap people often often do. Just accept what I said because I want to move on to the other issue that actually is a problem.
I do not have immune system issues, but I do have issues with acne and I'm friggin' 38 years old
(oh yea "It's a teenage thing!" whatever!) History nutshell: I generally had a buzzcut until I started shaving permanently at 25 (dear god that was nearly 14 years ago and yes I have been having mid-life crisis flare-ups lately). In my late teens I would often think I had ticks on my scalp but it always turned out to be sore acne pustules. When I had hair the broken zips would weep puss and make dried up crusts in my hair.
Shaving my head
significantly reduced the severity of those zits and their sensitivity, but head shaving
substantially increased the acne's appearance to others since it was no longer hidden by hair. I also have severe dandruff and I believe the shaving process allows the skin to be cleaner since it scrapes away the dead outer layer of skin. If I forgo shaving for a couple days my breakouts get worse, and if my skin gets moist I can scrape my fingernails over my head and dig up a crazy amount of dead skin. Unfortunately you cannot simulate the benefits of shaving by buzzing your hair. If you want those benefits you have to shave it to the skin and deal with the visual consequences. Sorry!
One thing that I noticed that increased the severity of the breakouts was stress. I don't know if stress itself increased the breakouts or if
a change in activity due to stress caused the breakouts, but I've always noticed they were worse when I was stressed. A decade ago I was working 7 days a week, but one day I was off so I hung out with friends and even they commented on the severity of my scalp's breakout.
Something that seemed to help my scalp was when I moved from a house with well water to one with chlorinated city water. Since the purpose of chlorine is to kill microbes it seems plausible that a nightly soaking in chlorinated water helps reduce acne flareups.
The next thing I noticed is the main thing: diet. I avoid organic whenever possible for various reasons (organic needlessly increases the cost of food due to hype and disingenuous marketing-by-scaremongering), but 8 years ago I substantially changed my diet from 90% junk food to 90% food of nutritional value because I wanted to lose weight, and my acne dropped to nill during that time. I think my biggest trigger is soda, and I've resumed drinking that stuff with a vengeance, and now have far more acne than during my water, chicken, and salad days. For me it really seems like the more of that stuff I drink the more acne I have. I apparently just don't care about the acne because it does not affect what I drink! You might have a placebo effect going on, but the truth is that junk food with the organic label on the box it is still nothing but junk food. There just isn't a way out of the fact that a human being must suffer and eat bad tasting food once in a while.

As for the gluten-free aspect of your diet I have no experience with that at all.
I also try to keep my head well-cleaned. If your immune system is compromised then this might help you too. I get these acne washes with sand-like granules in them that really seem to scrub the skin well.