I'm also 5w4d today and having those same cramps. I had my first sonogram today and they said everything looks fine, but the cramps do have me a little worried b/c it is my first one. My acupuncturist says it's just what you said, "stretching of the ligaments."
I'm also not feeling too sick yet! Thank goodness!
I only feel it accompanied with some dizziness if I don't eat like every couple of hours. I'm noticing though that I can't eat as much as I used to because my stomach seems to fill quicker and then I tend to feel a bit sick if I get too full. My best friend has an 8 month old and never felt any morning sickness at all during her entire pregnancy. Her mom, on the other hand, got sick before she even missed her period. I guess everyone is different and the symptoms shouldn't be how we regulate if everything is going okay. I do have to convince myself of that though because I've been questioning everything too!!
I don't know how to answer your Splenda question. I've been told to stay away from too many sugars. I'm addicted to Gatorade which I think I need to start diluting becasue it has tons of sugar. But personally, I'm not a big fan of artificial sugars (including Splenda).
Hope this info helped!