Hi Emma
Your breasts will feel super heavy and uncomfortable for a while, and most probably will leak constantly :p Don't worry. It is normal in the beginning and in a few days, the constant fullness will go away. After that, they will feel firm & full at the beginning of a feed or if you have gone too long between feeds. And in a few months, when your supply is well established, they will start to feel normal. Breasts are never truly empty. They aren't like containers. Instead they work on a supply-demand principle. So the more you feed, the more you produce & vice versa.
When you are nursing, it is a good idea to let her eat from one side first -- burp -- and put her back on the same side. After burping again, you can offer the next side. This way you are ensuring that she gets the fatty hindmilk and not just quencher. The next time you feed, start with the other breast.
It is so great that you are giving it another shot. I am sure that things will go smoothly this time. All the best!