I didn't notice any difference in the early days and I can't think of a pregnancy related reason why it would but someone may come along and say they had the same.
I started feeling uncomfortable around week 7-8 as my uterus was stretching and the only pain during sex was if my husband lay too heavily on my stomach, he's a heavy guy though. Obviously by this time I knew I was pregnant because had missed a period and done a couple of tests.
You can get 'bedding in' cramps but they happen at any time and not only during sex.
Hai I noticed that before I knew I was pregnant with dd, had implantation bleed which I took for af then started using opk cd13 got a positive and dtd and noticed it to be really uncomfortable/ painful, ( it was quite deep) didn't read anything into it till a doctor told to test so I'd have been about 6/7 weeks I guess