Hi F.,
how awesome that you decided to breastfeed Mia!
My son seemed to nurse all the time - he actually would literally nurse for an hour or two if I let him - day and night. It seems like I spent the first 3 months or so sitting on my behind nursing. But I gladly did it, because it is just the best way to nurture and feed your little one. Later I learned how to nurse lying down, and it was a life-saver because I got more rest, so you might want to try that (if you are not doing it already).
First of all to your question of having enough milk: the best indication of whether or not your girl is getting enough milk is the fact if she is growing and gaining weight. If she is, she gets enough milk. My son gained 7 ounces the first week (while most babies lose some weight initially), so there was never a question if he got enough milk. Some babies simply love to suck a lot. I used to say that Julian just liked to "hang out" on my breasts.
While nursing her, you can gently rub her back or feet to see if she stays awake longer to nurse more, if the issue is that she falls asleep too quickly.
Also offer her the other breast when you can tell that she no longer swallows milk regularly but seems to just suck for comfort.
In the beginning I used to think that Julian was actually eating the entire time while latched on, until I realized he was only sucking like other babies would suck on a pacifier.
You can change her diaper before you switch breasts, which will probably wake her up, too, and encourage her to eat more, if she is still hungry.
There are several teas that stimulate lactation. I used to drink "Mother's Milk", I am pretty sure it is made by "Traditional Medicinals", but I could be wrong. If you go to Sprouts or even many drug stores, check in their tea section for herbal teas that state they promote lactation.
And my final suggestion is that you could check out a La Leche Group in your area. Breastfeeding moms meet there to get their questions anwered, to get support, and to share what they have learned. I loved attending the meetings, because I learned so much, and later I was able to share with other moms what I had learned over time. I used to go to the Grapevine group, but there are several groups in the area. You can go to this link to find a group close to you: http://www.llli.org/Web/Texas.html
Enjoy your sweet baby, and enjoy the time she is nursing, it passes quicker than you think.
M.