Stomach always tense and tight

Hi I'm 12 weeks pregnant this is my 2nd child. My first child is 12 years old. So can't remember being pregnant the first time round. I was just wondering my stomach the last few days is constantly tense and tight. And seems to take hours for it to relax, is this just the muscles stretching. Is there anything I can do to help it calm down quicker. Keep thinking that maybe little babs doesn't like me being active but it can happen even at night time. Any tips would be greatful. Thanks