I don't know much about your relationship but a lot of Caregiver/dynamics are developed because it's stress-relieving.
From a domme perspective, it's very stress-relieving to be in charge of a little. It's comforting to be needed. It's relaxing to be a soft authority over another adult. It's fun to be around someone who is playful and carefree.
I imagine that it's the same relaxation type that a little experiences from being a little / in littlespace.
Do you two do a lot of online activities together? Like, say, play a couple of games together or watch TV shows or movies together? If not then maybe you should start up some Daddy/little date nights!
"Daddy, it would be super special to me if we could maybe get together next week or the week after and ... Can we do something like that Daddy, pretty please?"
Maybe he feels out of control. Maybe he would appreciate you being extra obedient or extra needy of him being in control of you. Even small things can help--like saying, "Daddy, I want to be super pretty tomorrow. Should I wear this pink shirt or this blue shirt?" Just, in my personal experience, those things really help to calm me because I feel like I am needed and have been given, like I said, a soft authority/control over the little.
Maybe he needs a little more silliness in his life from you too. Maybe try calling and leave him an extra cute voicemail to remind him that he is special to you. Maybe send him a silly little gift like your pillowcase so he can smell you at night and fee close. Maybe ask him if you two can do a candy exchange where you both buy treats and mail them to each other at the end of the month and get to share those things in a way.
In the end, you're probably going to need to address the recent frustration he's been having. Sometimes it isn't as scary to come to your Daddy and ask him, "What's wrong? I know you seem very stressed lately. How can I help? Can we talk about this, please? I care about what we have together and I want us to keep working together toward our happiness."
I'm sure you can get through this though. All relationships have bumps and maybe this is just one of those for you two lovely folks.