First of all, there is no form of emergency contraception
that you can take 2 weeks later. PlanB
, with which you may be familiar, must be taken within 72 hours.
Assuming regular cycles, the chance of conception occurring on cycle day #4 is very unlikely. That being said, women don't always know where they are in their cycle and things can get confusing, especially when you have concerns like yours.
Here is what you should do:
1. Take a pregnancy
2. If negative, repeat in one week
As far as your symptoms, these sound like they are cycle related and the most likely explanation is cycle related symptoms since the chance of pregnancy is so low. But just to be safe, you need to make sure that you are not pregnant as I recommended.