It's alright to have some caffine during pregnancy right? I'm around 8 weeks...?

With my last pregnancy I didn't drink caffine until after 14 weeks or so. But that was limited too, I would have a iced coffee maybe 2-3 times a week. And a can of caffine free coke. But now I want a can of coke or pepsi. I will not drink the caffine free for some reason it tastes different to me. I've been drinking sprite, seirra mist, ginger ale, 7-up, but crave for a darker pop. No coffee here, haven't been wanting any at all. Also what about diet drinks? I've been buying those sugar free packets that you pour into a 16.9 ounce of water. It has aspartame in it that is what makes me nervous, but i see SO many pregnant women drinking diet drinks.