Hi I become sexually active about a month ago and me and my boyfriend used a condom everything we had sex and he pulled out every time he ejaculated (came). This is my first period after becoming sexually active. First white stuff was coming out of me and then very little blood started. I don't understand why my period is so decreased than usual. Can you please help me

Of course you could be pregnant, since light spotting could be a sign of that, esp if it only lasts a few days. Condoms have a failure rate of about 10 percent and pull out while reduces sperm does not stop it completely.
But I am sure you were already aware of that. Women on birth control pills and condoms at times get pregnant.

So try a pregnancy test using the first urine of the morning.