Poor you - expressing like that sounds awful!
Im sure someone more knowledgeable will be along soon as I'm not very, but didn't want to read and run. You might get more help if you post in infant feeding though.
A few thoughts.....
I know that a pump doesn't produce as much as a baby so it might not be as effective as feeding "direct", and therefore not stimulating your supply enough.
At that age my DCs were feeding every 2 hours, so if you're trying to simulate breastfeeding with the expressing, you probably need to be expressing more frequently.
I think I'm right in saying that to increase milk production, it is not the amount of time you feed/pump for, but the frequency, and swapping between boobs regularly in one feeding/pumping session.
There is something you can do to do with breast compression that is supposed to increase supply, but not sure what it is - maybe google it.
I found a book called "Making More Milk" - can't remember the author, sorry, helpful when I had some supply issues.
Why does your baby have latching difficulties? Have they been checked for tongue tie? Are you not feeding because of pain or because you felt they weren't getting enough? Are you not feeding at all from the breast?Could you try again with putting baby to breast and trying to get more that way (see above about babies being more efficient than pumps, although I understand the latching trouble)
What you are doing sounds really hard work and to the outsider, not very sustainable (but I do understand the strong desire to to keep breastfeeding). It must be sapping all the joy out of having a new baby. Can you get some help in RL - seeing a breast feeding councillor at an NCT group or talking to one of the BF telephone helplines? It sounds like you need someone to look at the latch and baby and help you with that to get the original problem sorted out.
Hope things improve.