Boss doesn't believe I'm sick?

I have been out since Sunday and pretty much bed ridden til today with bronchitis. I went to the Dr. on monday and she was going to excuse me from work til Monday, but I told her I couldn't be off that long for fear of getting fired so she wrote the excuse til Thursday. Well my ociate called me and said my boss was saying how he really hopes I am sick and I'm not just running around. This really disturbs me, and pisses me off. He has been ill before, and upper management gave him trouble for it, so he should KNOW better than to even question my sickness. The only reason he is mad is because he may have to cover my shift, which I'm sorry comes along with being a manager, and getting paid more. I don't know if I should vent this to him or just keep it quiet, but it's a very messed up situation I think. If I need personal days I would have just taken them, it's not like I am getting paid to sit here coughing and hacking my lungs away anyhow. Should I say something? Even if I don't it was nice to vent this out here. Thanks for listening!