I am 13 weeks pregnant and started to have a bad, itchy, bumpy, red rash on stomach, chest, breast, arm and neck. not allergic reaction.

Rash: There are specific dermatoses related to pregnancy as well non-specific cutaneous eruptions (skin rashes). The most common pregnancy related rashes are PUPPP, Prurigo of Pregnancy, Papular Dermatitis of Pregnancy, Impetigo Herpetiformis and Pemphigoid Gestationis (most of these will occur later in pregnancy). A visit to a dermatologist may help to establish a diagnosis and proper treatment.