why is it getting worse each year?

I'm just 30 with two kids 3 and 6. I operate a daycare for the last 4 years and it seems every year when the snow comes it gets harder and harder to have the energy to shovel. Like my energy is limited and when I hit the that's it stage I have to stop right there and then and take a long long break before continuing. At my age that shouldn't be....should it?

I've been cleared two years ago for heart problems (which were done because I had palpitations to rule out problems, I have extra ventricular palps at times) and told I"m ok for activities.

I've prep a garden by myself in the fall and I admit over did it but normally a bath, relaxing and early bedtime would fix it this time it didn't and I woke up with my heart pounding painfully, I had to take several deep breath to calm it down and then it was ok but I had to take it really easy for a week and a half before getting my energy back.

They keep saying it's my anxiety but I'm not anxious when I'm doing those things.

So why is it getting worse each year?

I'm seeing my doctor today and will talk to her about it but a second set of oppinions is always good.