Constipation help

My 15 month old has been constipated for months now. More than 7 months I’d say. I’ve done everything: prunes, remove dairy, rice, banana, increase fluids, give pears, mango, papaya, etc. Etc. Still nothing. He is currently going on 8 days without pooping. I’m so stressed about this and doctor keep telling me that as long as he doesn’t seem uncomfortable, he is ok. But 8 days without poop when he regularly eats tons of solids. Anyone on the same boat? I’m dying here and scared for him.