Hey, I am still in first tri, but on my 3rd baby and this time round I was aware of them from about 6 weeks. I noticed it after sex, which is a very common time to get one. Obviously I can only feel them from the inside and not the outside, but it was one of the reasons I took a pregnancy test.
I tend to feel one just after I get into bed most nights, I guess because I am lying still, otherwise I probably wouldn't notice this early on.
In my previous pregnancies I did not notice them this early, but was well aware of them by 4 to 5 months in.