The belly tickling actually strengthens the abdominal muscles, which are really important for the horse and the back muscles, they have to work together.
Saddle fit, I would say is the #1 problem I find in my practice, and I realize its tough finding a really good fitting saddle, but it will cause alot of problems, and the horse is so good at compensating that you may not know you have a problem until it just blows up. And then it takes more time to heal.
The adjustment may not be holding especially if the saddle fit is bad, but what about your posture and seat? If you are out of balance, your horse may be compensating for you.
Sorry to get too into it, I am a biomechanics junkie.