I started running at a little over 200 lbs. I don't think I felt self conscious because I was too d@mn tired and out of breath to care what anyone thought.
At 185, I ran my first 5K race. Right before the race started, I saw all the skinny chicks in the spandex shorts and sports bras and thought " My god, what in the heck is a fat girl like me doing here? " I was sure they must be thinking the same thing. ( In all reality, they probably didn't give me a second thought. )
The race started, and one by one, I started passing those girls. By the end of the race, I knew what they were thinking about me. They were thinking " There goes the chick that took 2nd place. "
Don't let what people might be thinking, or even what they're saying, stop you from doing what you want to do.