You could look into applying for FMLA. I didn't know you could do that for intermittent appointments, I thought it was just for extended time off, but apparently you can. I got in trouble at work for not giving 48 hours notice before my appointment. My manager said it wasn't too big a deal though because I wasn't going to make a habit of doing that, but that is when I informed her that I have been struggling with a "medical issue" for 2 years now and need to have frequent short notice appointments. That is when she actually recommended applying for the FMLA. Apparently you have to work at your current job for 1 year before you can get FMLA though... and I won't hit the one year mark at my job until October! Thankfully she is still understanding and has found a way for me to still go to all of my appointments without getting an occurrence counted against me.
Anyway, to make a long story short, look into to applying for FMLA. Even if your boss is unhappy about it, she can't doing anything it if you have FMLA!