I have installed all my favourites apps on my S3 and every few days, the phone becomes sluggish and unresponsive. I can`t use apps because it moves slowly, I can`t get into settings as I used to ...
Can I check which application process is causing this behavior ?
You should be able to if you go into your settings and go to application manager and keep closing your apps until the slow framerate stops. When you isolate that app try to avoid using it as much as possible. In some cases it might be the case that you have too many songs or pictures on your device this might also significantly slow it down.
I don't really think it's from pictures or other data you have on your phone. Check the app manager and see if any map is hogging an abnormally high amount of resources. Other than that, you can make a factory reset, look it up, it might help because it makes your phone as brand new.
You should be able to close the apps without going into settings. Perhaps, you have too many apps open. This could slow down your further use of apps. Your phones physical memory might be full and you will need to reboot the phone.
If you press and hold the button on the bottom of the front screen (the home button), you get a list of all the apps running at that time. Try to close all to see whether performance improves.
Other than that, I've found that leaving the flash on in my camera app caused performance issues for me and destroyed my battery life, even when the camera wasn't active. I also uninstalled games I didn't play anymore, and that helped my phone respond faster. Unfortunately, I still suffered from responsiveness delays when I received text messages or wanted to unlock my phone. I upgraded to the S5, and if this one isn't a marked improvement it will be the last Samsung phone I own.