Telephone 0870 444 8707 immediately to speak to a breastfeeding counsellor.
There is obviously a positioning problem which needs sorting. You may have been told by your midwife that the positioning is fine but many midwives are not qualified to tell.
In the meantime you could try hand expressing and feeding baby your milk from a sterilised spoon, syringe or bottle top. This way baby won't get confused before he has learned to feed.
Go through the basics of positioning again, tummy to mummy, wait for wide open mouth then quickly bring baby to the breast. Don't take your breast to the baby. The baby's chin should come to the breast first and if you can still se any of the areola (dark bit around nipple) it should be above the nipple rather than below.
If it hurts, break the latch with your little finger and try again.
In the meantime lansinoh cream can help.