Contractions OR Lightening...

...Cant make out the difference but somethings happening since the past 4 days.
Typically in the afternoon, my stomach hardens like a tight ball which is accompanied by sharp jabbing, tinging pain, like a very very bad diaorrhea or cramping.
I havent been able to time it coz once my tummy is tight, its stays like that for hours with sporadic crampings. Mom says, my tummy looks 'low' now!
Past 4 nights have been very comfortable coz I am sleeping for straight 4 hours at a stretch. I get up only once to go pee & have no problem falling asleep! My appetite has gone down. I have lost a lb & a half. Mentally I am calm & relaxed ...have no clue how I am going to be during L&D...keeping my fingers xed!