Well, first off you should be calling your son's pediatrician for this problem not a midwife in my opinion. While midwives are awesome your son should have his own doctor. It's probably just a blocked tear duct though. Use warm compresses and gently massage near the corner of his eye. My daughter had a very swollen eye that would fill with yellow gunk as soon as you would wipe it and we had to end up getting an antibiotic cream for her eye. It cleared up pretty quick after that.

If you are breastfeeding you can squirt some of your milk in the eye or on it. The antibiotic properties in the milk will do worlds of good. This may clear it up, with the additional wet cloth wiping.

There isn't much a doctor will do unless there is an actual infection. A blockage isn't an infection, it just means the eye isn't draining properly. This can lead to infection though, so do wipe and massage it with a warm wet cloth as monkey girl suggested.

It's nothing you did at all, so no guilt at all here. Blocked tear ducts are very common and generally can go away on their own without medication. If the eye is pink, then you will need to get a medicated prescription drop for the eye and it goes away after a few days.