HelenE, you're doing extremely well, even though you don't recognise it! The weight of a baby at birth is nothing to do with their later weight - it's more about how healthy their mum was during the pregnancy, so weighing 7lb 5oz at two weeks early is already a very good start.
It's true, IME, about babies taking a few weeks to 'wake up'. My ds was like that, but I only know this with hindsigth, and I was persuaded onto formula. Then with dd I was determined to stick to breastfeeding, and succeeded. Not everyone has massive supply of milk, but you can assure yourself that you will make as much as your dd needs, as long as you keep feeding her as much as she wants.
With ds I leaked, yet struggled to feed, but with dd I virtually never leaked yet managed to feed exclusively. It's not connected.
I did find that in the early weeks I had more milke than she was interested in in them ornings, so I expressed it and froze it. It really was droplets - I would save a day's worth of ebm and freeze it in one go, all 3oz! But the supply built up in the freezer, and it was helpful.
If you're still concerned, try taking fenugreek. You can get it in capsules from healthfood shops. I took about 6 x 500mg capsules/day for 2-3 weeks at a time, on-and-off over a few months and am sure it helped to increase my milk. Here are a couple of helpful sites.
Breastfeeding online
Kellymom