Implantation cramps?

I missed my pill for about a week during my period and about 4 days after because my year  prescription ran out and I was out of town. 
I had sex on the 9th, a week after my period, didn't take my pill until the 10th, my ovulation date was the 14th.
This last week, about 3 days dpo, for about 5 days I've been experiencing cramping throughout my uterus. I've also been noticing my legs are lightly swollen after I come home from work about 8 hours into standing, and I haven't done anything different diet or excercise wise. My job schedule is the same it's been for months.
I haven't been too terribly tired but this last Wednesday I was so exhausted I couldn't get out of bed. By the end of my shifts I'm starting to feel really worn down. I also got sick last week and couldn't hold it down when I smelled my husbands food cook on the 12th and couldn't go to work the next day. I've also been pretty constipated this last week as well as bloated.
My period isn't due until the 31st and I never, never experience cramping this early in my cycle, nor do I experience the other symptoms. 
Could it be implantation causing the cramping?