I am 18 and I am supposed to start my period in the next few days. Instead I got spotting, then it stopped, and I spotted today again. I do have occasional sex, but it's always protected. What could this mean?

1 It can mean you are spotting and will have your normal period in a few days.
2. it can mean you are spotting will miss this period for some unknown reason and will get your next period next month as normal
3. it can mean you have an infection, a STD, some other illness
4. It can mean you are pregnant.

No way to tell without a full medical exam.

First you use protection ? What types, I assume you use more than one, if you don't want to get pregnant ?

Condoms by themselves have a 3 to 10 percent failure rate, so if that is the only protection, then you well could be pregnant.
But even using birth control pills and condoms there is still a small percent of error, less then one percent but pregnancy still happens using both methods.

So now you wait, really nothing else to do.

If your period comes, great, if it does not come, you wait another 10 to 14 days and then do a pregnancy test, ( can't do one sooner that is really valid) Use the first urine of the morning as soon as you wake up.