TTC but husband makes excuses

We used to have sex at least every other day. Only been together 18months, married for 5 months. Now we are TTC. I have quite a high sex drive and always initiate sex, I'm getting so fed up! I've tried sexy undies, pics, dirty texts, etc to get him in the mood before I get home. And NOTHING! I can text 'I'm so horny, I want you as soon as I'm home' the reply 'ok'. It drives me nuts! He's always too tired, headache, feels sick, too stressed etc. I'm so tired of being turned down. We even had a huge row the other day because it is my fertile week, I don't tell him any more to take the pressure away from him. He was tired and felt sick, I burst in to tears and explained the importance of having sex when we get a positive OPK. He said no and slept on the couch. The next night I hoped to catch my last chance this month, he said no he's not in the mood, so turned off the light and rolled over. Next thing I know he's looking at his phone- I could see in mirror reflection, (pic of a naked woman on porn hub) he then came over and started to initiate sex!! I did it but only cos I'm ovulating. I've not gained weight, still look the same, and act no different! He tells me I'm beautiful, is affectionate, buys baby things in his excitement of TTC, and is very loving. But with sex he just isn't up for it any more, what do I do?!!! Sorry for the rant I'm just struggling and no he's not cheating and he won't. It's a new thing and I'm asking advice to get him in the mood. TIA.