My advice, based on personal experience to anyone suffering from these problens is, as follows:
Buy toiletries, laundry soap and cleaning agents that do not contain any perfume.
Discard fabric softener and use vinegar instead.
Wash all garments, bed linen and towels that smell of perfumed washing powder in as hot water as possible, rinse with vinegar on a cold cycle, then repeat the cold cycle without vinegar. Afterwards run the empty washing machine on a hot cycle to get rid of any residue.
If you have to use a tumnble dryer, clean and rinse the filter before drying your clothes.
Keep a diary, where you make a note of what you eat, drink and wear every day for a month. It may help you pinpoint what causes flair-ups, thus indicating what you actually are reacting against. With the evidence of your diary to hand, it should be easier for your GP, dermatologist or specialist dealing with allergies to see what is causing the trouble.
Be very firm with friends and family who assure you that you cannot be allergic to their clothes, perfumes, pets, tobacco etc. etc. etc. You can. People can be allergic to anything under the sun and to the sun itself!
It is a lot of work tracking down the source of itching, etc. but worth making the attempt.
If antihistamines work, fine, but they are only dealing with the symptoms not curing the problem, and many people find themselves sleepy or dopey when taking antihistamines.