pregnant with 2nd baby

Hiya I'm pregnant with my 2 child 1st child is 19 months can't really remember the pains I had with her but was putting Christmas tree up today and don't know if I pulled a muscle or not (didn't life anything heavy) but all day I had a constant full ache not anything really sore but it wasn't like period cramps it was the kind of pain you do get when you maybe pull a muscle in your belly, just wondering if anyone else has got this and what could it be stretching or something?