I am by no means an expert, but if you're feeding him every hour to hour and a half, he might not be getting a full feeding in. At seven weeks, he should be able to go longer in between feedings. Is he getting full feedings each time you put him on? By full feedings, I mean is he nursing at least 15 minutes on each side? Or, is he falling asleep during the feeding. Regardless of how much you pump, other factors may affect how much you produce - lack of sleep, etc. Also, if you're putting him on to nurse too frequently (and not resting!), your body doesn't have time to rebuild your supply in time for the next feeding. I would highly recommend On Becoming Baby Wise, great book and was a great resource for me with all three kids.
All that being said, you may just not be able to produce enough milk for him, and that's okay. If you're not able to breastfeed him, you're not a failure as a mom - okay????
Hope that helps, keep me posted!
: ) Becky