Usually I say if you have to ask, you are. But that's being harsh and judgmental, so I'll answer this in a different way.
Answer:
A girl is a slut, according to Merriam-Webster Online Dictionary, if she is a) slovenly, b) a prostitute or c) saucy. For those of you who aren't up on your British vocab, slovenly equals dirty, in the I-haven't-showered-in-three-weeks kind of way. So, to find out if you're a slut, just ask yourself three simple questions:
HAVE I SHOWERED LATELY? Or you could rephrase that as, "Do I look good?" I'm going to go out on a limb and guess that the answer is "yes," because most men don't want gross, smelly women, and you've gotten quite a few men. But if you can answer yes to this, you aren't a slut (technically).
HAVE I BEEN PAID FOR SEX? If you can answer yes, you're a slut. Now, most people who could answer yes here will find excuses not to. So let's be honest: any kind of sex -- oral, anal, boob, etc -- and any kind of payment -- cash, diamonds, dinner and a movie -- count. That's not to say that all dinner-and-a-movie dates that end (or begin) with sex are prostitution -- most aren't. But if there's a direct relationship between sex given and gifts received, that's a bit on the slutty side.
AM I SAUCY? Now, here is where Merriam-Webster and I disagree. I like being saucy. I think it's fun, quirky and demands great fashion sense. But I do see where the saucy-slutty relationship comes in -- saucy girls get guys. What they do with them is their own business, but the potential for sluttiness is there. So, if you answer yes to this question, I'll let you off the hook and say you may or may not be a slut. Use your own discretion.
Of course, you do have to keep in mind that the Merriam-Webster dictionary is rarely consulted in rumor mills, and most people just go by their own definition. While you may be able to say, nope, I'm not a slut and I can prove it, the great majority of people will probably say, "Well, my definition of a slut is a girl who sleeps with a lot guys (like, say, seven). And you've slept with a lot of guys, so you're a slut." Whether you're a slut or not, there's really nothing you can do about that definition.