Do you have a local BF support group, or somewhere a trained BF counsellor can watch you feed? My DS is 19 weeks and I've recently been wondering if he has a tongue tie ( long story! ). His latch has been slipping a bit and he seemed more fussy and less satisfied when feeding. After posting on here about TT I was recommended to get someone to check his latch first.
I went to our local BF support group, the lady who runs it watched me feed and said we had a couple of positioning issues. It sounds silly, but was mainly down to the fact DS is now longer, so you need to adjust how you hold them slightly. I wasn't having any pain though so may be different for you. I felt a bit stupid going back to basics this far down the line but she said its quite common at this stage. Worth getting checked if you can, it could be something that's obvious to an observer but not necessarily to you.
DS also has two teeth, which can affect things. He dribbled and chewed for weeks before there was any sign of teeth so it could be early signs of teething.
hv came over yesterday and changed the positioning so he was sitting up on my lap more as he was still lying down like a baby and being very awkward and heavy to keep there while feeding! seems to be much better now - better on my back at least!
Wouldn't you think it would get easier as they got bigger?! I've been trying feeding lying down for the first time, easier on my back but just makes me fall asleep! I've borrowed a book and gone back to basics but DS seems set in his ways now, he's determined to dive in nose first and squash into me. Still, he's gaining weight so it must be working for him!