Hi Shabina,
First, take a deep breath
Take a couple of days off; don't read anything related to PMP and the exam, to recharge and refresh yourself. Try not to think about it either during those two days.
After two days, when you feel a little refreshed, you can pick up an exam.
Based on what you said, stamina seems to be your big hurdle right now.
So we can maybe first focus on building that up.
The way to build up that stamina is practice, practice, practice.
If 100 questions is your current tipping point, try doing 110 questions next time under simulated exam conditions.
Once you feel you can do 110 with reasonably good concentration, try 120 and then 130 ... don't worry about the complete paper at this point in time.
Our aim is to first build up the stamina.
Try this for a week everyday and see if it helps.
If are you able to build up to say 170 then you can start taking full tests again and this time I'm sure your stamina would last much longer than the current 100 questions.
It's like working out, you start with light weights, but consistency and continuous progressing is key.
Try this and let us know of your progress. We're here to help.
Oh and finally, don't do anything PMP related for at least two days before the actual exam.