Take a deep breath. You aren't alone! Trust me, I know. I have a six month old baby girl and a three and a half year old son. It is a trial. But you can get through it. One thing that often works for me is to take a "mommy time out". Your kids can do with out you for a few minutes while you cool down. Make sure that they are in a safe place and then go in the other room for a few minutes. It may sound odd or horrible, but I have found it is a lot better than falling apart or blowing up. Then you can go in and deal with it.
At about two and a half years my son stopped napping. It can be hard and there are some days he gets very tired when he doesn't have a nap, I try to get him involved in something quiet and restful instead. We read books, he watched the occasional DVD or documentary (he loves documentaries and shows on sea life), or we get playing with the cars. This keeps him calmer on days that he won't nap at all.
Another option is to go for a walk or do something else that will help your child expel their energy right before nap time. This will make them more likely to nap cause they will be more tired. Fresh air is great to help out with this.
Just remember...breathe! You aren't alone!