Hello dear, brief answer, it is most likely urticaria, detailed answer, I have gone through your question, and I feel your history matches with urticaria, a type of allergy, difficult to point out the cause, foods, Food additive Color,dyes,,preservatives, drugs,house dust mites, insect bites any source of infection in body, like worms, ringworm, sore throat, Urinary infection, gut infection, viral infection, or may be autoimmune (e.g.seen in thyroid disorder above mentioned are common causes , there are tons of many other also. and in many cases , reason may not be found, so look for the cause of urticaria, You can take antihistamines like levocetrizine 10mg at night time for controll of itching, take that for at least 2 weeks than as per need, , you may need investigation also if it still persist thank you