WiggleyWorm, definitely call one of the breastfeeding support agencies and talk to someone over the weekend, it can be helpful to talk through what you're doing and it also will make you feel better that you're taking some action towards achieving your aim to breastfeed.
Does it hurt the same amount on both sides? Can you see any damage done to the nipple?
If you think you've damaged the tissue, you could try nursing just on one side for a few feeds to give it a break.
Have you tried sitting in front of a mirror while you latch? Sometimes you can see a positioning problem more easily when you're not staring down from above.
Or have a look online for the symptoms of thrush and if you think you (and/or DS) might have it get to a GP as soon as poss.
Try to ignore the negative voice in your head, you are doing a brilliant job, are very brave getting through that pain (I remember it distinctly, used to dread every feed) - that phrase 'if it hurts you're not doing it right' is not helpful. You are doing fine getting milk into your baby, but ideally it would be good find a way to feed where there isn't agonising pain and hopefully getting a bit more milk into your baby so you start seeing DS gaining wweight. Getting expert real life help is a good start, don't worry about dissolving into tears, the HV or breastfeeding counsellor will half expect it and won't think that you're crazy, just upset about an upsetting experience.
I hope you get the help you need, I experienced horrible pain, and did get good MW support, found a breastfeeding support group, called counsellors etc. In the end I bought a nipple shield and after talking through using it with a counsellor used that for several weeks to give myself a break from pain and kept getting my latch looked at. In the end me & DS just got better at doing the BFing dance together and it stopped hurting after a while. I used to dread the next feed coming, and then feel like a terrible mother for dreading feeding my child, it was just a matter of taking it one feed, one day, one week at a time. DS is now 5 months, exclusively breastfed and I enjoy and am proud of what I achieved. The thing that kept me going the most was that I didn't want my enduring memory of breastfeeding to be pain and knew from reading posts like this, that it would get better.
Big breath now, and call someone.