At your age, it is common to have occasional irregularities in the menstrual cycles owing to disrupted ovulation secondary to the failing hormonal
balance as it tries to get on track. You are right in thinking that two periods in one month may have caused the delay at present, but, things need to be substantiated through clinical evaluation by a specialist and investigation, more so because you are sexually active using barrier contraception
which has a higher failure rate. Please get an assessment of the serum beta-hCG
titres and also a trans-vaginal sonogram to clarify the situation. Hope this helps.