Are Lighter And Shorter Duration Periods Symptom Of Plan B?

Hello. About 1.5 weeks ago my period ended and about 1 week ago the condom broke midway through intercourse, we immediately switched to a new condom and we are pretty sure nothing happened but just to be safe I took the Plan B One Step pill 2 days later. All of the sudden today I have been bleeding like a normal period. When I was taking birth control pills, I recall having occasional spotting in between periods but it was usually much lighter than this and not so soon after a period had just ended. What does this mean? Could it possibly be a side effect of the Plan B One Step pill and if so how long should it last? What else could it possibly be? It caught me off guard today and scared me a little.