BTW, don't be too alarmed, also real contractions do not ease up when you sit down or change positions... but braxton hicks contractions do.
Yeah sounds like BH contractions. They get more intense if you've been more busy and active than usual. :) They can be uncomfortable, and sometimes even hurt a little.
Could be Braxton Hicks - they can be brought on w/ movement (walking etc.) and can get painful toward the end of the pregnancy. If you experience 4-5 of these within an hour, be sure to head to L & D to get checked out though.