Am I just being hormonal or should I be worried???

So I'm pregnant and live with my boyfriend and I can't tell if I'm just being hormonal or if he's just making me feel crazy... I've gone through his phone a few times before and have gotten upset about him messaging someone he used to be with saying pretty much he still had feelings for her but didn't want to have those feelings anymore because he's with me now. And the other day I looked through it again and some girl messaged him asking him if he thought she was hot and he didn't tell me about it and I asked him about it and he got super pissed off at me and started yelling at me for going through his phone again, but I feel like I kind of have a valid reason to go through it??? and plus he changed his password and won't let me have it now because I've gone through it before. I feel like I have a good reason to go through it though because for one, I'm pregnant and need some type of validation sometimes, and 2 he was messaging his ex and tried hiding it from me and was denying it even though I saw the messages. any advice??