Colds suck... but they suck even more when it's your third week of college. I've been sick for about 4 days now, but today was the worst day. In high school when you wake up feeling sick you can stay in bed all day, eat soup and popsicles and watch re-runs of your favorite shows. You can do the same thing in college except anything you miss from class will not be handed to you the next day in a nice little packet.
The first thing to do when you know you're getting sick is to review your syllabi and see what your professors attendance policy is. For example, attendance in my math class is required, you only get one unexcused absence; but in my economics class attendance is not required, nor is it accounted for. If you know you're 8am the next morning has required attendee then you have to prepare the night before: drink lots of water and make sure you get to sleep early.
If you're classes the next day do not require your presence, you'll still want to get the notes for that day. A lot of professors don't want you to email them about being sick, they likely have thousands of students and any number of them could be doing the same thing as you at the same time. Instead, check the syllabi to see if there are any notes or power points posted online. If not you can try and get the notes from another in your class, or you can visit your professor during office hours. If you read ahead in your book, or in given readings and find out what the professor is going to be talking about that day, and write down your questions, you can ask your professor to help answer them.
It is best to stay in and rest if you get sick in college. If you work yourself too hard you could develop pneumonia, and if you stay out too much you may also be at risk of infecting others. If you can take a sick day then do it! you'll get better much faster and be back on top in no time.