How to help a constipated 5 week old

ka

My son just started new medication for his reflux and he’s also taking has medication. Poor guy has been a mess for the past week and a half. I noticed last night he seemed to have a little relief because he slept for 4 hours straight and the past few days he hasn’t been able to sleep AT ALL. But..... this morning he has been grunting and straining and when I changed him he had like three little poop pebbles that was the consistency of clay. His doctor won’t be open until Monday. Any advice on what I can do to help him until then?