Pain while nursing

✨JBR✨ • Married for two years. Nanny. We're expecting our first baby in March!
Started yesterday, when i nurse on one boob, I feel an intense tightening feeling at the top of my other boob. 
Please help! It hurts. 😓😔😕
FTM, my daughter is 4weeks, I'm breastfeeding and supplementing with formula. (She was a preemie).