battlefield 4 fps drops

when i play bf4 no matter the quality 90 fps normal but after less than min in game my fps starts dropping like crazy from 90 to 4-15 for a second and then back up my pc is fx 8320, 7870 ti 8 gigs of ram watercooled cpu gpu card doesn't go more than 60C i tried to stop cpu from parking cores i oc-ed a few times nothing i don't know what to do this is happening  since the game came out for pc