DD, now 6.5months, was born at 5lbs11oz, and while she gained weight really, really well for the first month or so - 8oz a week - since then she's put on about 3oz a week, except for a fortnight when we were abroad - she fed more when she was jetlagged, put on about 4oz. She's teetering on the edge of the 2nd percentile. She bf feeds for about 5-10 minutes, about every three hours during the day - something like 7am, 10am, 1pm, 4pm, 7pm and 11pm. She is a very content baby, and she sleeps really well. She doesn't fuss after a feed.
At the baby clinic, our HV kept on muttering that she wasn't gaining well, that I should give a supplementary feed, but DD just isn't interested in feeding often, and she won't take a bottle. So I just panicked, but a panicked mother trying to force a feed on a baby who isn't hungry isn't a great combination for stress-free living. I tended to get weepy and hyper-stressed, and it took me weeks to get over a visit to the baby clinic. At which point it was usually time to go back to have her weighed... I read all the Kellymom stuff, too, and none of it seemed to make a difference either.
Finally, we were referred to hospital for crossing 2 percentiles. DD was measured and weighed and examined, and the doctor asked questions like did she throw up a lot. DD doesn't. Anyway, the doctor said DD seemed healthy and there was no reason to believe there was anything wrong, that some babies just follow their own curve, and to come back in three months, once solids were established. Of course, DD isn't interested in more than four or five mini-tastes of solid food at a time.
Anyway, I think it's really hard to trust your baby to know what is right for him/her. But if you don't think there's anything medically wrong, then I think you just need to back down, take a deep breath, and try not to panic. I know it's hard, DD fed really badly today, and it was hard not to panic and try to shove her onto my breast. But follow your fears to their logical conclusion: does your baby have other symptoms that might suggest an underlying problem? Dry skin is really common. Is he going to starve? No. Is he failing to thrive? No.
It sounds like you've had a really tough time with the surgery, try to give yourself a break from worrying, things aren't as desperate as they might feel. Maybe your baby just meant to be small for now. A friend's baby only takes 2-4oz a feed, is on 9th centile. She was referred to hospital, too, but told her baby is just taking what she needs.