Is there any kind of virus in my phone?

[Android Central Question]

I have a Samsung Galaxy J7 Prime 16GB. I don't know when it started but since i updated my phone to Android 7.0 Nougat, there are some ads that simply pops into my phone. Like, i am doing absolutely nothing, just looking for my screen and then BOOM, an ad appears! Sometimes an Image Ad and sometimes a Video Ad. And there is the thing i did not understand, when the Video Ad pops into my screen, i click the "Recent Apps" button and appears the ad and a symbol of Nougat. Is it something about Android 7.0? Is it normal or i am with viruses? [email removed for privacy by Mod] Thanks.

Obs.: Not only ads appearing. Eventually i open my Gallery and there are some Screenshots that i never took before. Screenshots like my HomeScreen or a Video that i was watching... It is very weird. Please help!