Discharge??

So I'm young, and I've had my period for 2 years and like 4 months. I'm in 7th grade and still don't really get the whole concept of discharge. Like how do I know it's healthy, or if something is wrong? There's days where there's little to none, and days where there's a lot. I've also noticed that when I wear underwear that is kind of loose that I discharge more, or at least it seem like more. I know that probably doesn't make a whole lot of sense but bare with me here haha. How long is it supposed to last, is it okay that when my boyfriend and I are like making out and doing shit that middle schoolers do that I discharge a lot?? If someone could talk me through these things it'd be greatly appreciated 😬🙂