There could be many reason for that:
The CPU speed of your device is 1.2GHz meaning it can process apps at a decent speed, but when multiple apps demand the CPUs processing at the same time, that's when your phone will throttle and freeze...
[] Try closing all other apps including games and browsers.
[] Download and run CCcleaner for andoid:
https://play.google.com/store/apps/details?id=com.piriform.ccleaner&hl=en
[] run only 2 or 3 apps at the same time (remember that your android device is already runs a "few" at the background. so adding more applications will surely bog it down.
'''You might want to consider devices with higher CPU speed in the future (do not mind marketing gimmicks like quad core CPU, octacore cpu, for most application what really matters is the CPU speed)'''
hope this helps