burning sort of smell

So i was driving to school this morning with the heater on when i get this horrible um fart smell and I thought it was the area you know so I turned on the recirculate button and then it started to smell like burning and im paranoid ( my old car had a smoking problem lol) so I turned the air off and left it alone til it got cold again so I turned it back on and sure enoough it smelled like fart again . and then burning after i hit the recirculate button so im like screw this and I put my jacket on and left the cold ac on low til i got to school. Im pretty sure im not farting without knowing and lighting a fire with the recirculate button but what could that be? I just hope i dont find it burned when i get off ha ha thank you!

I noticed lately with mine if I turn the heat on I get a burning smell. I took a look under the hood and there's oil leaking onto the engine. Could it be burning oil?