Am I reading too much into it or being ignorant

​So last night I came across a msg on a snapchat app my husband now uses. Never used the app before and only uses it to contact a female "co-worker".  When I asked (and it was just a casual question at that stage) he snatched his phone back and refused to let me see anymore. He had to delete it. What ever it was. Then tells me later he was talking to girl from work about work stuff but didn't wanna tell me who he was talking too cause he "knows I get funny about her" I really wish I kept my mouth shut so I could view the messages later and know the real truth. Why use snap chat? Is it cause the messages disappear?! Why not use nessanger? They're friends on Facebook. 
​I went for a drive earlier just to get away. Parked my ute up and sat there thinking. He's started having interest in doing weights. Then there's our sex drive. He still shows "some" interest but when we do have sex he takes ages to get off then driving back from a meal last night (before any of this happened) I asked him if sex feels weird for him because it does for me at the moment. His reply was "it feels like my dicks in a whole lot of nothing" .....of course I'm gonna "lose/r" after having our first child 15 months ago. Topping it off in about 6 weeks into my second pregnancy. 
​I don't know what to think. He says there's nothing going on and I should trust him but I'm confused. I need to talk this out with someone but I have no friends or family where we live at the moment. We've moved to victoria from tassie.  Could I be over thinking this?....