Hello, I am totally
Welcome to the board!
my millk supply was low at 3 weeks too because i only started EP at 15 days or so. I found with pumping every 2-3 hours, 30 min a time, I ended up with tons of milk in the 4th or 5th week. It took that long, but keeping at it means you can build it up (some women take that long regardless).
You are definitely in a position to build your supply still even if you didn't pump or nurse for a few days. Milk supply doesn't establish itself until 8-12 weeks and even at 12 weeks you can increase supply. You are at a good start using a hospital grade pump and double pumping but you probably need to pump more frequently to rebuild your supply. Make sure your flanges are fitting properly and try going up or down a size if you need to.
Try to pump at least 15-20 minutes every 2 hours even if you aren't getting much right now. Try to pump once between 1 and 5am and if you can throw in a power pump, you'll probably start to see results faster. It will be exhausting and you may find yourself extremely frustrated for a few weeks. You may be crying and wanting to quit every day. This is normal, just try to take it one day at a time and focus on the total number of pumps you managed to do instead of the total number of ounces you collected.
Consider getting a second set of parts and store your pump parts in the fridge between pumps to cut down on washing. If your LO won't latch but will comfort suck, you can try to single pump one side while he sucks on the other. (This was sometimes the only way I could pump since my LO wouldn't use a pacifier) The more often you pump, the more prolactin will be released to increase milk production.
The key is to trick your body into thinking more milk is needed. The more you pump, the more your body thinks more milk is needed. Any stimulation to the breast and nipple helps. Doing massage and compressions while you pump, and between pumping sessions can be helpful.
Taking Domperidone could be helpful, it works best if started in the first 12 weeks post partum. Check out www.drjacknewman.com and www.lowmilksupply.org for lots of info about milk supply and how to increase it.
Get lots of rest, drink lots of water, take prenatal vitamins, eat lots of nutritious, fatty foods and sleep any chance you get. Let the housework slide. Clean floors are over-rated ;)
Good luck. It is hard work but can be rewarding. If it doesn't work out and you have to give up, be proud of yourself for trying. I would just strap on the pump and sit with my laptop reading posts from this site. It really helped to get me through to read about tips, tricks and stories