Said I had dentist appointment as an excuse to go to interview...my job now wants to see a doctors note

I've been unhappy with my job of nearly 2 years in a small business, and have finally started applying to positions in the last month. I have had pretty good luck with getting interviews, which is good and not so good. Last week I ended up being 20 min late one day, and and 40 minutes late another day due to an interview and followup interview for different jobs. 2 weeks before that, I took a sick day for an interview and also was late one day due to an actual doctors appointment. Neither interviewing process worked out...but that's another issue for a different thread. I was going to take a break from applying to jobs due to the lateness factor, but ended up applying for a very desired position that had just opened up. The day after I applied I got a reply asking me to come in for an interview. The interview is next week, and I sent an email to my boss saying I had a dentist appointment and would be 1-2 hours late. They replied saying to bring a doctors note. They have never asked for one before, so they must be suspicious. I'm at a loss in how to deal with this. Has anyone dealt with a similar situation or have any idea what I should do?

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