I'm 18 weeks and mine are still growing. With my first child, my boobs grew more after I had him. I would buy bra extenders and nursing bras in a few different bigger sizes.
Mine stopped around 16 weeks have started hurting again now at 30 weeks. Been wearing nursing bras and bought a full size larger bra than I usually wear just to get relief!
They can hurt your whole pregnancy. Get some good bras, you will need them. I went with jogging bras in two sizes larger than pre-pregnancy.