bf is cheating need advice

I have a gut feeling my bf is talking to other girls but I need to get proof before I confront him. 
It's a gut feelings with things he's does...
He's changed his password on his phone
He keeps his phone turned upside down
Once his phone went off wen I was by him and he covered it really quickly until I moved.
I logged onto his Skype and he had been talking to a girl on there but when I went bk to screenshot it it had gone
I think he's using some sort of dating site I don't want to make a profile but how can I catch him out also what are the common dating site in the uk? I think he might be chatting over Snapchat which I'm no good at.
So need some advice ladies on how to catch him out pleaee
UPDATE:
I found the evidence I needed he's on the dating site badoo 😭 I haven't confronted him yet as he's not here. I'm so upset and pissed off I feel like I've just wasted the last 3 years of my life!!!