Pilates is the key also mix in some yoga. After you play, ice up your back to reduce swelling as well. You can most likely get some excersises off the internet. The reason I suggest pilates. Is it works the small muscle groups (stableizer muscle) as well as the larger groups.
If it is a simple strain then treat it with Rest, Ice, Compression and Elevation (immobilization in the case of the back.) I don't hesitate to take an NSAID like ibuprofen or naproxen when it hurts. Sometimes when mine is more severe or doesn't respond to RICE then I contact my chiropractor. This usually does it but, sometimes it may take repeat visits and sometimes a therapy massage. If it takes more than 3 visits to a chiropractor, then you probably should see an Osteopath, you could have something more serious than sore muscles or a strain.
Once the pain subsides, Rescue is on the right track. Pilates for core strength and daily stretching, especially before throwing should keep you strong and loose.
telling ya, Pilates kicks a$$. You'll be huddled in the corner sucking you thumb and begging for mercy. After going to PT after my millionth back injury, I tried Pialates. I was pain free for almost a year, before I lifted one patient to many and had to call it quits.