Did you add any Apps? if so try deleting them one at a time to see if it stops.
Or reverse thatg and delete all and add one at a time. It may take a while to see which one may be causing the problem. The other issue is memory overload if you run apps that require more than you have.
Worse case the OS needs to be reloaded.
__________________ If someone helps, tell them by clicking the Thanks buttonî