You might have a nutritional deficiency (perhaps caused by a food intolerance that has caused damage to your stomach lining; maybe celiac disease) and/or a sensitivity to certain chemicals (such as sodium lauryl sulfate, and/or such as other chemicals that remove oil from skin).

I have a couple pitted nails, and I don't seem to have any psoriasis. When I stopped using SLS and started a gluten-free diet, my nails at least stopped getting worse. I don't know if they're getting better (but the one that had been developing gunk underneath stopped, and I think they look a little better than before). I thought it was nail fungus at first, but the doctor was skeptical. We'll see if this helps overall, though.

Do you have any other symptoms? Do you have gum recession? Sodium lauryl sulfate sensitivity could be at least partly responsible, if so.

Do you have known digestive issues (gas, bloating, distended belly, nausea, etc.) or problematic stools of any kind (i.e. oily, mucus-laden, overly smelly, extremely large, green, diarrhea, constipation)? If so, I would consider celiac disease even more.

Do you have skin problems that aren't psoriasis? e.g. acne, really dry skin, eczema, or such? What about growth issues?

Anyway, just some food for thought. I hope it helps.

Also, I might recommend researching minerals—you might be getting too much of one and inhibiting another.

Also, if you are or were recently pregnant, that might be a factor.

I've heard that nail biting can be a symptom of a certain mineral deficiency. I forgot which mineral, though.

Blood in stools is another stool symptom.

Now, as far as whether any disease or condition matches your symptoms, I've just discovered something (and this likely helps me, too): Alopecia areata

It can cause hair loss and nail pitting (both of which I have: several ways for the hair loss, including very small patches on the scalp and beard areas, receded hairline, bald lower calves and ankles, and such).

Anyway, even if this is the case, that's not to say the other suggestions won't help at all (especially as they don't really know a lot about this condition, what causes it and how to treat it, though they do know some, it seems).

See this article (it talks about how many people with this also have celiac disease, and how often hair regrows on a gluten-free diet): http://celiacdisease.about.com/od/symptoms ofceliacdisease/a/Alopecia.htm

Both this and such as celiac disease have links with thyroid disorders (hypothyroid for this, and either kind for celiac). That could be responsible for your weight problem and irregular periods. Do you get cold really easily or have other thyroid-related symptoms?