The morning after pills is a large dose of hormones, so it can cause some side effects. I had only a moderate reaction to the morning after pill. It cause severe period like cramps for about 2 days which I've never had anything like before or since. I also suffered from bloating, nausea, and a headache. (Although the headache and nausea could have been stress related from being afraid I was pregnant). So it may be possible you're suffering from side effects combined with stress. Because the morning after pills isn't full proof, it is also possible you're pregnant and it was just too early to tell. So I would retest if your period doesn't come.
However 7 days is a long time to be suffering. If you're not getting any relief, you should make an apt with your doctor just to make sure everything is ok.
The morning after pill can cause a lot of side effects, including cramping, back pain, along with nausea, headaches, bleeding, and so on. Wait until your period is due and then take a home pregnancy test again if it does not show up, although the morning after pill can change your normal cycle and cause you to have your period sooner or later than expected. Also, just so you know, the morning after pill is not meant to be used more than twice in a whole year, so make sure to always use another form of birth control when you have sex.