Why is my phone doing this recently?

[AC Question]

My brother downloaded an app thinking it can modify Pokémon Go and I kept on getting ads ever since. But I decided to factory reset my phone and now I experience lag( the phone freezes for like 5 seconds) and sometimes when it freezes it takes me back to the lock screen please help.

 

[B. Diddy]

Welcome to Android Central! I'm guessing that app was downloaded from some unreliable app source, and not Google Play Store--that's a great way to get malware. Avoid doing that kind of thing. Also, trying to hack or cheat at Pokemon Go is not condoned here, so I am closing this thread.