My son is 8 months old now, about 4 days now he hasn't popped...?

It has been about 4 days now my sons hasn't yet pooped, the 1st day i was giving him a bath and he was tryin to pooped,so i was takin him out but only one little pebble came out,then later on that day he was tryin again and he was having a hard time then he started drying! and it continued that way, tries but nothing comes out!I do not have prunes,gripe water doesn't do anything! yesterday mornin it was bout 8am and he juss all of a sudden startin screaming from in his sleep, so i was changing him and he was trying again,so i was trying to help him by holding his ankles and his thighs are against his chest but he wouldn't push anymore,i never tried helping him i mean using my thumb or my pinky,i do not want to,i might hurt him or something! What should i Do??