Allergic reactions will not cause itching symmetrically on both legs. Likewise, there are no skin ir internal diseases of which I am aware which cause symptoms of the type you describe.
When people itch without a rash, stress is often a factor. At times it's the itch itself which induces the stress--in other words, the more you itch, the more you scratch, and so on. And the more you worry about whether you're going to itch, the more you will.
You can use a topical anesthetic, as often as needed (even every few minutes.) This can help break the itch-scratch cycle.
Over-the-counter anesthetics include: Benadryl, Lanacane, Sarna, and pramoxine.
Use one or more of these and use them regularly, until you stop itching.