Mobile Game starts lagging after a while when playing on my phone!!!! Pls Help!!!

Hello all,

I have a finished game that I want to release on Google Play. I downloaded the .apk to my phone using unity and did some play testing. I found that the game would start LAGGING over time. In the beginning, I had around 60 fps (used "Application.targetFrameRate = 60"). After playing a couple of rounds of the game (it is an endless runner) the frame rate dropped all the sudden and reached about 35 fps and became unplayable. When I had quit the application and the started it again, I once again only had 35 fps. If I quit and force it to stop, then start it again I also only have 35 fps as before.

If I close the game, and wait 5 - 10 minutes just doing other stuff on my phone, it goes back to 60 fps when I start it again.

This is so weird. I don't understand how the lag can just appear and then persist when switching scenes and restarting the game even.

Someone please help me, I am completely clueless!!!