Although factory resetting the phone and reinstalling all the apps helped a bit, it really didn't help from app crashes, phone's relatively slow performance to my expectation. All I did this time was flashing my phone back to stock rom. Had downgraded the OS back to the state having OS and build # when it was bought originally. Now my phone has Android version 4.1.2 and build # 12.0.A.2.254. Have been using it for 3 weeks now and I should say it is absolute beauty. Haven't had any crash reports, response is instantaneous and smooth operation from the moment I touch and start using the phone. Guys, my advise to you if you are looking for a solution to this forum is that.. Just don't update your system if you have bought the phone brand new recently if you have happened to have updated your phone already.. Just flash it back to stock ROM. You should be able to Google and know how to do this.
I realize now why Sony hesitates to release Kitkat OS for this phone and now I get a strong feeling that they will never release an update to Kitkat OS. I wish they don't! Thanks and good luck everyone!!