Just after christmas, while pregnant, I picked up DPs phone to take down his sisters mobile number. The tab left open was porn. DP had always said (without me expressing any feelings either way) that he doesn't 'do' porn and wanking and that he only ever had when his marriage was failing as he feels it isnt much different to cheating as you're still getting off over a person other than your partner. He had expressed this many, many times. When I saw the porn open, I was surprised but not particularly bothered. However, out of curiosity I checked his browsing history. There was loads of porn, every single day. Often while I was putting the children to bed, he was in the toilet or I was taking the children downstairs in the morning; it was constant. We had got engaged at Christmas and was having sex every day so I was shocked to see the extent of his porn watching.
I casually mentioned that I had seen that he had porn open on his phone and that he didn't need to cover it up or pretend it wasn't something that interests him if it was. He swore it was the first time in years and that he'd only done it to help me out because I was ill 
He was really keen to emphasise this was the one and only time. That then made me feel crap because I knew how much he was lying.
Our sex life went a bit downhill after the baby but we DTD about a month ago. It was over very quickly, i think due to all the masturbation. He talks about sex a lot and I think he could have a sex addiction. Since we slept together, I have had some odd symptoms. I have had abdominal pain, stinging down below and (apologies for TMI) greeny thick discharge. I'm terrified he might have taken a step further and cheated, then passed something nasty on to me.
He is a policeman and so works long and unpredictable hours. He has a history of lying over things (he 'forgot' to tell me that his exW had called her new baby by another man by his surname and had been telling people he was his) and flirty behaviour. When we first met he was ill and messaged the nurse saying it wasn't the same being home without her to look after him. At a work Christmas party he chatted and flirted non stop with a friends girlfriend and pretty much ignored me - he blamed drunkeness.
Today I wanted to google the weather forecast but my phone was in the babys room and she was sleeping so I picked up DPs phone. When I pressed the internet button it came up as a secret tab and all browsing was secret - there was no history. This just makes me think he's hiding things again. I have spoken to a friend who has urged me to see a doctor and thinks I am right to be suspicious but my sister thinks I have been unreasonable to have ever looked at his phone and that he's entitled to privacy.
What do you think?