I would suggest having her speyed (desexed) to prevent this from happening in the future. Having her desexed can prevent health problems and by the sound of it may be helpful for You.
This sounds like the "nesting period" there is a very high chance she is pregnant and preparing somewhere to have her kittens.
1. A change in behavior when a cat is pregnant is normal. I would be more concerned if her behavior didn't change. Provide her with a secluded place where she can give birth and nurse the babies, That is what she is looking for.
2. As soon as her babies are weaned, have her spayed. Once the babies reach 2 pounds, have them spayed or neutered.
3. Keep her indoors.
When a cat is pregnant it will usually behave this way. She is now looking for a comfy, safe and quiet place to bring her babies out. Hormonal changes take place and so you will notice more and more a change in her. Congratulations. You are going to be a granny.
Oh.....you will have to take her in for a check-up with the vet. I'm not sure if you know this but STDs apply to felines as well. Stray cats have not only that but also parasites that could be potentially dangerous for both mom and the kittens.
I am assuming your cat has had her rabies and other vaccinations...so we can rule that out. Is there some reason you didn't get her spayed? There are low-cost spay and neuter clinics but I just realized you live in Pakistan so I don't know how prevalent those services are in your country. Hopefully the symptoms she is showing are related to her pregnancy, although I hope you know she can still be spayed at this time, depending on what your plans are for the kittens. Will you be able to provide homes for them once they get here? It's something to think about. Good luck with whatever you decide.
thanx alot for responding to my problem..they were quite helpful to me and i will follow these instructions and be careful in future...thank once again P.S she is regularly vaccinated and de-wormed...