I have been worried about the same thing as while im stressed with my 3 kids or rushing on the school run, moving house, and xmas stuff to do im getting really painful braxton hicks everyday. I went to see midwife yesterday and she did a scan just to make sure my cervix was closed which it is so im guessing theres nothing to worry about apparently after multiple pregnancies your uterus tends to be more irretable and you feel everything worse then with say your 1st.
Keep your mind distracted as much as possible. Pick up a new hobby just not a hobby that is physically or mentally stressfull. Start a scrap book or journal make it fun for yourself to keep you less stressed!