What are the reactions in the first few days of pregnancy? In the first few days of pregnancy, the hormone levels in a woman\’s body undergo huge changes, and the body will experience a variety of discomforts. Common reactions in the first few days of pregnancy include breast tenderness, nausea and vomiting, headache, backache, etc. Breast Swelling and Pain A few days before pregnancy, many women will experience breast swelling and pain. Breast swelling and pain are caused by stimulation