Why is my iphone acting so weird?

Hallo,

Lately my iphone 5 is acting overly strange.

When I'm next to it, it suddenly is typing out of nowhere. And it's always typing 'space' or 'b' or spamming 'm' and 'n'.

It's really annoying because sometimes when I'm playing a game, it suddenly touches every place on the screen and goes nuts.

I've already did a software update and 'cleaned' my iphone on the inside so that maybe the virus would go away, but it didn't help.

This never happened before, I don't understand.

Also when I charge it, it looks like he has its own life.

When he wants, he charges. When he doesn't want to, he doesn't.

I can't go back to the store because I have bought this iphone from someone else, but I find it strange that it's acting like this out of the sudden.

Thank you