Should I quit my job? [I Need Advice]

I'm a full-time nanny for a 1 year old girl. It's not a hard job but I'm on my feet often and I do outside activities with the baby. This is my favorite job so far! However, I struggle with a heart problem. I just got insurance so I go to a Cardiologist in less than 2 weeks. This problem makes my heart pound 24/7. My heart rate is always higher than normal. I can no longer have caffeine, sugar, lots of carbs, or alcohol. I can't climb stairs or hills or even walk for too long or I'll get chest pain. I have shortness of breath and sometimes I get a squeezing tight feeling near my heart. I've been to the emergency room twice and they've said my heart rate is high but they cannot find anything so just follow up with Cardiologist. I can't afford to not work as I just moved into an apartment 3 months ago and my boyfriend can't financially provide for both of us. I thought about trying stay at home work but I don't know anything about it. I cry at the idea of quitting but I also feel I'm pushing my body too hard. Thoughts??