Hi D.. I am a Certified Breastfeeding Counselor and hope what I suggest will help.
First, I think you were given some bad advice. Babies cannot and will not thrive on nursing only every 3 hours. By the same token, you will never make enough milk by nursing every three hours. My best advice for this situation is to demand feed giving unrestricted access to the breast. This may mean baby nurses every hour sometimes. It may mean she just wants to pacify on you, or comfort nurse. These things are all essential to maintaining a sufficient supply. Scheduled feeding for a breastfed baby will not ensure a good supply.
Many Moms here are suggesting you pump to increase supply. I advise against that. A double electric hospital grade pump is only (at best) 50% effective at emptying the breast. When you're talking about sending signals to your body to increase production, the breast needs to be emptied. Pumping will not do that. You need to get your baby to breast as much as possible. Only the baby is 100% effective at emptying the breast. Spend a few days in bed with her. Settle in topless and allow her as much access to the breast as possible, even if she's just dream feeding. Wear her close in a sling or wrap when not nursing. Just having skin to skin contact has been shown to increase supply. If she is sleeping in a stretch longer than 2 hours, then I would pump in between to keep some stimulation going, so that you still have milk available when she wakes. You can top her off with formula 1-2 oz. at a time if she needs it, but do this last. Always offer the breast first and keep her suckling as much as you can. Say she eats at 2pm and nurses for 30 mins. Then say at 3:00 she is fussy and wants to eat again. Nurse her again, even if its only been 30 mins since she finished eating, THEN use formula. Even if you feel like your breasts are empty, they are never truly empty. She will get some milk and in turn stimulate you to up production. Then you can top her off as needed, little bits at a time so she needs to eat again soon, so you can nurse again! Its hard work, building a supply, but you can do it and it takes just a few days. This can be done but you have to be diligent and give as much stimulation to your breasts as possible, and then more. You also have to remember that baby will go through growth spurts where she will want to nurse like crazy. This doesnt mean you arent making enough, just keep nursing. Its how she signals to your body she needs more. Its normal and only lasts a few days at most. It happens at 7-10 days, 3 weeks, 6 weeks, 3 months, 6 months, 9 months, and 12 months.
In the meantime (and I know you have mentioned already doing some of these things), but here is a list of things that help.
Oatmeal
Brewer's yeast: sprinkle it in your oatmeal, eggs, sauces, soups etc... and don't worry, the whole family can eat it and not lactate!
Fenugreek
Blessed Thistle
Mother's milk tea: You have to really drink a lot to see a huge difference, but combined with other methods, it will help
More Milk or More Milk Plus by Motherlove Herbal Company: This comes in tincture and capsule form and contains fenugreek, blessed thistle, nettle and fennel. All of these combined help with milk production.
Goat's Rue: this is used in women who have PCOS, low supply due to underdeveloped mammary tissue, adoptive mothers, etc... sot his is good stuff. It can make an adoptive Mom lactate! (used in conjunction with other herbs and medicines) More Milk Special Blend has all of the things listed above plus goat's rue.
Reglan (by prescription): this has had some nasty side effects for some women, but some women have had great success without the side effects.
Domperidone: (by prescription) Many doc's wont give a script for this because you can only get it overseas. But I do know a few women who got a script and had it filled.
Here is a list of Motherlove products (No, I don't sell them or work for the company. I have used their products and recommend them often to nursing Moms who have had much success with them.)
http://www.motherlove.com/products_extracts.php
Here are a few articles about low supply:
http://www.motherlove.com/faq_lowbreastmilk.php
http://www.kellymom.com/bf/supply/low-supply.html
http://www.lowmilksupply.org/
http://www.kellymom.com/newman/b-protocol_increase_bmilk_...
http://www.kellymom.com/bf/supply/decrease-formula.html
If you need any further help, please private message me. And if all else fails, I recommend seeing an IBCLC. Good luck D.! I know you can do this!