Advice on opening up more sexually

I’ve been married to my husband for 6 years, we struggled to conceive for three years, had one miscarriage and two babies in that time. My youngest is one now and our sex life is finally getting back on track. My problem is, I’m so hesitant to open up more when it comes to things like sexting (which he loves to do since he works night shift) and just generally spicing things up. I really want to do more for him I’m just not sure why I have such a mental block when it comes to trying to be “sexy” for him. We have great sex, some might call it vanilla, but I’m generally happy with that aspect of it. We have sex about three times per week (doesn’t sound like a lot but he is only home at night 3-5 days per week) and I always have at least one orgasm, most of the time two. When his texts lead to anything sexual at all I freeze up and change the subject. I don’t feel comfortable sending any sort of pictures to him even though he asks me to. The problem is, I don’t feel sexy at all. Any advice on getting out of my comfort zone?