Hey Lacey, I have had a bit of a back issue (from a Mtn Bike injury) that seems to flare up with the SUP from time to time.
Physio has given me a heap of stretching exercises (as well as strengthening) for the gluts and hamstrings. Most people have very tight hammys and this places extra load on the lower back.
She has also given me some exercises for one of the weird lower abdominal muscles (forgotten its name) that apparently is the key to stablising the hip (hip flexor) area.
I am trying to do them every day as I find the older you get the more maintenance is required to allow you do the things you could do at 30

PS it is rooted after our club comp the other day - grovelling in small surf puts a lot of stress on it!!