Bill,
You could of over practiced cause I have shot like that several times and a few days later had back problems and needed to rest up..Now I had my L5 S1 rebuilt so to speak with a pc.of my hip bone and a disk replacement and Hardware that is still there so I know what caused my pain and need to take it easy...I'm 48 years old and lets face it we like shooting so much it's sometimes hard to put the bow down...The best thing I can suggest is to see your Dr. and explain your pain and let them scan you to just make sure there isn't something going on down there...You could be starting to break down so to speak and Marine or not we ain't built to last forever in this life but for some the afterlife here we will get our new bodies that will never break down...So for now get it checked out cause I'm no Dr. but take care of your back...God Bless and thank you for your service...Keefers <><