We put our Julie on Lamb and Rice food. We use the Sience Diet/Natural. We can only find it at PetCo and it a little more expensive but well worth it. No GI problems due to food, and no hair loss since.
The only time Julie has any problems is if she get ahold of people food, we had some friends over on a Saturday and one of the kids must have given her something she should not have had because by Sunday she was vomitting and Diarreha so bad, that she had to stay the night at the pet hospital. It was so sad to see her so sick, but as long as we stay on the Lamb and Rice food she does really well. If this does not help, you should see your vet and get their take on what might be happening.