Boss needs doctor's excuse. What should i do?

I had a 24 hour flu, and had to miss one day at work. My boss told me, I can not come back until I get a doctor's excuse. But, i feel completely fine, I took some nyqiul, and now I feel perfectly fine! I dont have money or health insurance to pay for a doctor's visit, for me to give me meds that are probably do the same thing as nyquil! What should i do?!