Hi S.,
My daughter was 2 1/2 when my son was born, and to top it off, my son had surgery at 2 months old. Needless to say, potty training came to a screeching hault!!!
So, we tried many things . . what finally worked was putting her on the toilet every 15 minutes and making her try to go. (It also helps if you LOAD them up with their favorite drink on this day). The next day, we spaced it out to every 30 minutes, etc. The third day every 45 minutes. You should be able to tell by the diaper/pull up how often your child is going. Also, when you do this, put him in big boy underwear. If he should have an accident, you will know right away rather than in the pullup which draws the wetness away from the skin. You can adjust your timing by knowing when the accidents happen!
Everytime my daughter was successful, she got to put a star on a chart for #1, and a bigger sticker on the chart for #2. The chart was a calendar I quickly made on some posterboard. She got to put all the stars for that day into the appropriate day's square. When daddy came home, he looked at the chart and praised her for all the times she went potty that day.
I know it sounds like a big pain - my 2 year old is about to go through it. I just haven't gotten the motivation to do it with him, so we are procrastinating.
Good luck!!! It's great when they can go by themselves, just make sure to monitor the cleaning habits also!!!