Plan B

2 days after my last cycle I had a condom break during sex. Later that day I took the plan be needless to say my cycle for May is 15 days late!!!  I'm starting to panic a little.. I read that emergency contraception can alter your cycle... Has anyone else experienced this? When should I take a pregancy test. I might add that I do not 'feel preganant' I say that bc the last time I concieved I experienced preggo symptoms within the first two weeks..