Doggy Style?

I lost my virginity a year ago and so far my partner and I have tried a couple positions , which we both like but some more than others.. 
Point is that I barely let him try doggy style with me and he's always asking for it but I just can't! It hurts and it feels like I'm about to crap out of my vagina , and not so much hurt its like a lot of pressure down there and after he's going at it for a minute I stop him and we have to switch to something else because it also feels like my A Hole is about to let loss and fart up a storm . And no I haven't told him that I'm a little embarrassed 
, I also don't like how it feels like his trying to take my intestines out I hate the feeling .. How do I overcome this ?