J.H.
First of all, good for you for being so dedicated!! I didn't mind the pumping (though I did sort of feel like a cow), but I didn't have to do it so regularly. Some people just don't make a ton of milk...don't beat yourself up about it! It is okay to do formula when you are at work--you shouldn't feel so bad--they make formula that is very close to breastmilk now. Think of how it was when we were kids...my mother in law told me she used to give my husband evaporated milk from a can!!! And he's fine (mostly! haha)!
I would say, use what you pump when you are at work for that long stretch on the weekends (I assume you must have to pump then) and then supplement with formula the rest of the time...and go to bed at 10:00pm if you are tired. :)