Hi my 1 year old has not pooed for 3 days. Any suggestions to help him poo soon?

My boy don't like vegetables and fruits too so he also easily constipated. I tried give fruit juice like orange juice etc but he took a sip and don't want to take a second sip. Until 16months he still refuses alot of fruits. I tried giving water too but he won't take much. So I added a small amount of glucose grape powder into his water and he drinks more. Also I change his milk formula to dumex which helps too maybe less heart. If not every 3 days he will s*** and cry for a long time.