Hello and thank you for the replies.
Yes frequency is the main issue, but I can see how that happened. Our sex life declined pre DC when he was going through a particularly stressful time at work. It was still a lot more within what is probably the "normal" range - definitely a lot more frequent than it is now anyway! Once I discovered I was pregnant we stopped completely. He didn't like the idea of it while I was pregnant. I wanted to, but I understood his feelings and was ok with that. Then after the birth, I had a few problems and it took about a year before I was ready for penetrative sex (and as that is all he will do that meant another year of celibacy). We tried a few times but it was too painful for me.
At some point over those years of less sex I think I realised a few things... he had never played with nipples, never performed oral sex on me (or anything in the way of foreplay in fact) but I had always on him, and a general lack of intimacy - for example he would rarely come to me for a cuddle (I'm sure it wasn't always that way), but if I ever went to cuddle him it would result in him iniating sex. So we would go from weeks of zero physical contact to full sex and I wanted some kind of middle ground.
I spoke to him about some of the things - well actually before I'd said anything at all, during sex one time he played with my nipples of his own accord - that was a pleasant surprise and I told him how much I enjoyed it. He did it on one other occasion after but never again. He also began using his fingers on me without me asking or saying anything, and that's something he has continued doing the few times we have had sex, but he doesn't put them anywhere that feels good.
I have tried to guide him to the right places and said where I like but he always veers back to the same spot...so I just leave him to it now and try to hurry him along. 
I asked him about performing oral sex on me. He did it once, told me he didn't really like doing it and wouldn't want to again. Afer that, any enthusiasm I had ever had for doing it to him stopped, so I stopped.
With the cuddles=sex thing I brought that up outside of the bedroom. I told him how alone I felt. I said that I felt it was always me going to him and that sometimes I would like cuddles to just be cuddles and not to go further. He made an effort for a few days..touching my arm and hugging me a bit more but that soon tailed off. I stopped going to him for cuddles so much, and when I did he often wasn't really enthusiastic in response to them...said he was afraid of me thinking he always wanted sex. I tried to explain that I did want sex sometimes I just didn't want to go from weeks of nothing to full on sex every time we cuddled. He didn't seem to get it, or it didn't change anything.
He now seems back in 'cuddles=sex' land and I have stopped letting that happen so much. It is only me who goes to him and maybe 3/5 times I will say no if he tries to go further.
Sorry that's really long - I do know the position is the least of our/my worries, but it puzzles me the most. When I thought back I realised it had begun before I got pregnant, and before I had ever even thought about the things mentioned above. At the start of our relationship we had sex a lot more often, I'm pretty sure he was more loving in general and we definitely did it different positions. I don't understand.
I used to cry at night because we'd go to bed and he'd literally turn his back on me and go to sleep. I grew to hate the sight of his back.. I know that's stupid. I tried really hard to make an effort back then, but it was not returned and eventually I stopped, and as I said I have reduced the amount I cuddle him and also the amount I let my cuddles turn into sex. So I understand that part. I just don't understand why he won't look at me when we do, do it. I really don't think he could be having an affair. He works from home. When he does have to go to the office I am pretty sure that's where he goes, and he calls me throughout the day just like he always has.