Am I afraid to be happy?

So a little back story. Me 21F and my partner 22M have been together for 5 years. Our relationship is healthy, loving and we do work extremely well. The only thing is that I’ve always suffered massively from anxiety more specifically in the last 2 years health anxiety and well he is a very happy and positive person that very rarely feels anxious or depressed but  still knows how to comfort me in difficult times. 

So fast forward to today and I’m doing amazing on the Health anxiety front, I’m not worrying/obsessing over my health anymore and I can finally say my mind is clear of those things. The last 6 months have been the worst in regards to that and I hate to say that it did take its toll on my relationship, he felt like he couldn’t help me, I was always in a horrible state of worry and panic to the point it crippled me and in the end turned out to be making my partner extremely unhappy. We nearly broke up. He said he thought I needed some help and that if this carried on for much longer he doesn’t want it to change the we he feels about our relationship. This conversation we had really opened my eyes to how this anxiety was effecting my
life, my relationship, my work and even family so I promised to go and talk to my doctor and I did. I was prescribed Zoloft and I’m still waiting for the counselling but I’m in such a better place mentally and feel so much clear minded now and my relationship has been thriving like it did before. 

The only thing now tho is I’m starting to develop abit of anxiety around the fact that my partner makes me so happy and my life right now feels so happy to the point it makes me nervous and almost makes it feel suspicious and I’m noticing that I’m trying to find things that are wrong even when they are not, like maybe how my partner might say or do something and I’m like “is he still happy? And is he just not telling me that he’s not?” Or if someone even talks in a different tone or says something they wouldn’t normally say I’m thinking way to far into things thinking that those things point to something awful. 

Why can’t I just accept that things are going well and stop creating this sinking feeling as if something is happening when it is not?