hello..thanks for your query..
From what you describe,I feel that you have something knows as Acute Urticaria
.It is common condition with frequent exacerbations and remissions.In most cases,a direct cause is not identified.However a combination of correct anti histaminic tablets for a few months help in reducing the severity and frequency of these hives
I assume you mean Birth Control Pills by saying bcp.If it is something you have used for so long, and haven't changed the brand you take,i don't think that should be the cause.
Start application of a soothing anti pruritic calamine
lotion to relieve the itch.In certain cases a few bood tests are advised to rule out ant internal causation of the same.Do not worry,although symptoms and treatment course of urticaria is prolonged,these do not pose any danger in most people.
hope this helps!!take care...