How can I tell he's cheating ?

I'm worried how can I tell ? Not sure if it's my pms driving me crazy or if my 50 year old hubby is cheating ???

FYI I'm 32

UPDATE!!!

I'm so stupid!!

Ok yesterday I caught him taking to a women while I was on the phone with him and when I asked who's that ?? He got nervous and got off the phone with me I was like hell no !

Bu we share the same email and got a confirmation email last night about a family trip and the lady puts at end

Ps, I hope you and your family enjoy the trip , hope she's not to pissed off at you to enjoy her self ! Told you she didn't do good with surprises!