I'd say allergies if you have no rash-like symptoms (otherwise I'd say eczema.) Bed bugs could also be another possibility-- but they do bite and will leave marks. Lice is another option, but if you get a comb and scratch it at the baseline between your hair and your neck, you should pull up eggs if it is lice. Be sure to google what they look like in the event you have dandruff so you don't send yourself into an unnecessary panic, haha. ALSO dandruff can cause itchiness and that is just dry skin and it can in fact make you scratch your head nonstop. Dry skin can also be further irritated by allergies so... yeah I would take an antihistamine or something like that. See your doctor uvu
When is the itching worst? Do you wake up in the middle of the night itching? Are there any bumps / rashes on your skin?
Sounds like allergies. I wouldn't take anti-histmaine until after you've seen your doctor. You don't want to mask any symptoms before he can diagnose you.
My suggestion: take warm showers and baths, try to keep them short. Use some skin care soap, and if you can take baths, add some oat to hydrate your skin, and it could help with the itchiness too. After that, like some people have said before, use a moisturizer on the "itchiest" parts of your body. I wouldn't advise just taking benadryl or anything else, cause it could make you drowzy and it's a bit risky if you drive/at work. Always check with your Doc first =)
@(you need an account to see links) In my opinion, definitely allergies. I can attest to how they can come out of nowhere, at certain times of day, etc. I have been dealing with serious environmental and some food allergies all my life, and from your description, that's what it sounds like. If it's something chronic, your allergist can give you allergy shots (usually once a month for 2-4 years straight) which can get pretty expensive, but it is extremely worth it. Prior to having the shots, I would get massive hives all over my body if I even touched grass or certain plants, but after the shots, I haven't gotten a single hive in 2-3 years. If it's not something chronic, he/she can just prescribe you some antihistamines which also help a ton.
Benadryl should help. Also try calamine lotion. You may have a mild case of eczema. Keeping your skin moist is a good idea, but sweat/moisture can cause eczema to start acting up. The only reason I'm going the eczema route is because of the itching on your head (among other areas). Eczema can be irritated without having (you need an account to see links), as well as showing up in rashes or bumps.