I have red welts that appeared and when i scratch it spreading it itchy?

Trigger: Dryness or an allergen irritated the nerve in skin, scratching activates histamine release by resident skin cell, making all worse. If not infected apply Benadryl (diphenhydramine) cream or hydrocortisone.

Dermographism: This sounds like a physical urticaria, not an allergy. Best approach is to see a dermatologist do not take Benadryl (diphenhydramine) except as a sleeping pill. Ceterazine ( zyrtec) is much safer , much more effective. You may also benefit from a prescription cream.