Hi welcome to HCM,
Usually a change from 7-5days in menstruation
is not something to be concerned about as long as you bleed fresh i.e. red color. Since you and your boyfriend have not used any type of contraception
this could be the result of you getting pregnant.
I would recommend you to take a over the counter available pregnancy
test and even if that comes out to be negative please consult a Ob/gyn doctor at the earliest and avoid sexual intercourse till then as it could be harmful if in case you are pregnant in the first trimester.
Thanks and hope this helps