Hello Scorpio,
Welcome to our Pain Management Community. I am delighted that you found us and took the time to post a question. However I'm sorry to hear about your pain - buttock I assume?
Ppl that have an issue with their SIJ (Sacroiliac Joint) often experience pain when sitting. The condition is called SIJD (Sacroiliac Joint Dysfunction). Indeed it can be the first SX (symptom) of the condition. Walking more, getting up often and changing positions frequently can be of benefit. Now this can be a mild condition and never get worse or require intervention - if you avoid things that trigger it - like prolonged sitting.
It may not be your SIJ at all. Your gluteal muscles may just not be accustomed to your new position of sitting. I find sitting on the floor cross legged can ease the discomfort I feel in my "sit down" area. Indeed it was suggested by a D.O. (Doctor of Osteopathy). Heat also helps. NSAIDs can be effective - but before taking a NSAID (like Ibuprofen) please consult your PCP.
I am hopeful that you will let us know how you are doing - and that something you heard here has been of help. If you have additional questions please feel free to ask. I'll look forward to hearing from you again soon - and often.
Best of Luck,
~Tuck
Yes, you can become sore from sitting too much. You did have a very physical job for a very long time so your body is not used to sitting.
You say it hurts to lay too? It might be time to see your Dr for a checkup.
In the mean time, it might help to get up and walk around a little every 15 minutes or so.