Wow, do I sympathize. I'm 21, and pregnant and the baby's father and I literally had *** once this past spring semester at college... and as they say, "it only takes one time". He was never really a part of my life, and lives 2 and a half hours away. Nobody needs to know this, but EVERYONE asks. Normally, I just let people assume. It seems to be easier to let those that don't know you nor care to know you assume what they want and let it be.
I had a stranger at 7-11 say, wow you're about to pop - but no wedding ring? I said, absolutely not - I'm a lesbian! and walked out. Which was a lie, of course, but I laughed.

I think the best way to get through it is with a sense of humor. People tend to be idiotic and rude. Don't let it get to you.