I've just started taking biotin. I try to drink 2 quarts of water a day. I haven't noticed any extra oilness or any acne but I have fairly dry skin to start with and was never very prone to breakouts. From what I've read some people have had breakouts with it and dropped to a lower dosage and the breakouts stopped. You may be taking to high a dose for your body as well as not drinking enough water.
Biotin is water soluable vitamin and the only way you can flush the excess out is by drinking enough water. If you don't drink enough water to get rid of the extra it shows up as breakouts and oily skin.