M.B.
As the others have said, it's possible to relactate! The sooner you start, the better!
A lactation consultant would be incredibly helpful, and the La Leche League is free.
There are a lot of things you can do to start milk coming back in, but the best one is to put the baby to the breast as often as possible. The baby is more effecive than the pump at bringing in milk, though pumping will help as well. The following things are all great for milk production: More Milk Plus supplements (you can get them on amazon), Mother's milk tea, fenugreek supplements, eat oatmeal once a day, drink a beer (brewer's yeast is good for milk supply) and drink lots of water.
Good luck, mama! You can do it!