Why did she suddenly stop calling me?

I've been seeing a fantastic girl for about a month, and we had been talking nightly and hanging out up until this past weekend. Suddenly she stopped calling me alltogether. The last time we talked was over dinner on Friday night, and everything seemed just fine. I didn't do anything to make her angry that I'm aware of, and everything was just like normal at the end of the night... I know she has been busy with some issues with some friends of her's from work, but I can't figure out why just now she stopped calling me all of the sudden...I want to call her to see how she is doing, but I feel like if I call a bunch of times I'll just end up looking desperate....I've only called once this week, should I keep trying? how many calls is too many? Is it too early to panic? I understand that maybe she just isn't in to me after all, but to just stop all contact so abruptly seems odd...this sucks...