Do the red spots last for less than 24 hours.
Your history suggests that you have urticaria
If you have this problem for less than six weeks, then we will think of acute urticaria. If the duration is longer than six weeks then we will call it as chronic urticaria.
Oral antihistamines and topical calamine
lotion will be of help. The type of antihistamine and duration of treatment can be best decided by your doctor.
The blood investigations need not reveal anything. They may be normal.