My period is usually heavy n last 5-7 days. this time it was heavy the first day and light the rest n lasted only 5 days. now i've started spotting?

Several causes: It is not uncommon for women to have variations in their menses. Weight loss, stress, travel, illness, change in birth control, new medications, pelvic infections, and pregnancy can all cause changes in the menses. I suggest doing a home pregnancy test it pregnancy is a possibility. If you have no changes in weight, health,meds, lifestyle, you could wait another month to see if it regulates again.