What Causes Light Spotting During Periods Instead Of Heavy Bleeding?

hi im 20 years old and my period is very irregular and is always a very heavy period but the this month it was very light it was so light that i don't not have to use anything if i did not want to . and me and my boyfriend been try to have a baby so could i be pregnant . and i ask my family when they had there kids if they had a period to and my mother did and my aunts did to ..could you help me