How long can plan b affect your cycles?

Need a little help, took plan b some months ago. But when you look up information it only tells you what to expect for the first two cycles.

First cycle came a little late took a test came back negative.

Second and third cycle came right at it’s normal time.

This cycle I’m already 5 days late. Only cramps when sitting down. Took a test negative. Could this still be some side effects from the plan b.

Under some stress but it never effected my period before. Weight loss but it has been small amounts over time.

When would be a good time to call the doctor if things don’t change?