I had an over-abundent milk supply and used the 'compression feeding' technique to help my DS get to the hind milk. Basically you gently but firmly quezze you breast when the baby is sucking, to the baby it feels like another let down and the fast flow enchourages the baby to continue feeding well.
On the other side, if you are not already doing so, you could try and make sure you are eating as well as possible and drink pleanty of water etc. A lady I knew of had a v. stressful time when her baby was born. When things began to resolve and she got more rest, food water etc she was AMAZED just how much her milk supply improved by.
Good luck and if you do want to keep breastfeeding, be careful introducing formula because it can sometimes artifically 'stretch' babies tummy's so they aren't as satisfied by the next feed, also, just dropping one feed can effect milk supply quite a bit. Having said that the lady I mentioned, because her baby needed an op and docs wanted him to put on weight for this asap, advised her to do one feed a day with some special ultra-high calorie milk. She manged it well, but I know of other women who the introduction of a bottle feed or two has led them to stop breast feeding altogether.
Hope this helps. My baby put on weight but was very shakey at the start, dropping centiles for the first few weeks. With help, I sorted my positioning out, demand fed and offered milk if he gone a while without it. It took me ages to get my head around breast feeding but when I did, he rocketed through the centiles and easily got to 6 months on my milk alone which for me personally was what I wanted and was invaluable.
Good luck,