Missed period

So i’m on birth control and i started it in july. my last period started during active pills but i continued to take it normally, and no period came during placebo pills, because it came a week earlier. i went through another month & i started my placebo pills on wednesday and i got a little spotting on friday and only some spotting on saturday morning, but other than that my period hasn’t been the way it normally is. Is this just my period adjusting to the new birth control since it’s only been 3 months? or should i be concerned of pregnancy? (i had sex a month ago)