Measuring big

My last two appointments, my son is measuring 4 weeks bigger. Had a appointment monday. I'm 29 weeks and measuring at 33 weeks. My appointment at 24 weeks, I was measuring at 28 weeks. Is this happening to anyone else? What are you doctors staying about it? All mine is saying that if he keeps is up. We will have to do another ultrasound. It kinda scares me. I don't wanna push out a gaint baby..