Potty Training a Four Year Old...

So how was I too know how difficult it was going to be potty training a four year old. He tends to go every thirty minutes if you take him, but still doesn't want to tell you if he needs to go? I have taken over the duties for the next two days in order to Give Naomi a break, but I don't know if it is going to work. I have tried the reward chart, sticker after sticker, candy, toys and almost everything else you can think of. I have read the postings, blogs and other information, but I just don't know if I'm doing it right. Why can't my boy tell me "I need to Potty!" Is this really suppose to be so difficult and last so long. It seems we have gone four weeks now and we have some good days, but that is the days that we take him every 30 minutes. School is coming up soon and I want him ready by mid-august. Any advice would be greatly appreciated.