What are the laws in IL for bathroom access in a very small company?

I know it sounds stupid, but what are the laws in IL for bathroom access in a very small company? I'm the office manager of a very small company. I am generally the only person in the office. The office is located above a garage in the back yard of the business owners home. There is no bathroom in the office, and I am required to go into the house to use the bathroom. This isn't such a big deal, but the owner of the business is going on vacation for a week and expects me to drive down the street to go to the bathroom. He specifically asked me "isn't there anywhere else you can go to use the bathroom while we're gone?" I want to know what my rights are regarding this issue. He will not give me a key to the house while he's gone, and will not leave the door unlocked. What are my rights here? And if I decide to go to OSHA, first of all...will they even listen to my complaint? And second of all, am I protected from being fired for bringing this complaint to such an agency? I'm sure if somebody from OSHA came to inspect the office/property, they would find a lot more wrong than just a bathroom issue...