My 6 month old is super constipated

Hi FTM and i’m struggling. We have switched baby to formula since I am no longer producing and he has been eating purées for about 2 months. The last few days he has had clay like poops. Yesterday 3/4 was rough as he was trying to poop and was straining. I opened up his diaper and i could see the poop was coming out but it was a struggle. I have been in contact with his pediatricians office but they have no openings. His 6 month appointment is scheduled for Tuesday 3/10 but i still feel like that’s too long. I have done a warm bath, bicycle kicks, prune puree, a little bit of prune juice and water but I feel like it’s not working. I feel so defeated. He is truly a happy baby but once he has to go poop he is in pain. If anyone has some advice, i would greatly appreciate it! TIA