I think I'm having false labour contractions.. they are down in my lower belly. They come and go when they want. I was under so much stress today that I think it triggered something.. what do you think? And how long till the real ones come. Some one give advice about what is happeneing please.

How far along are you again? You may be feeling Braxtion Hicks contractions... think of them as practice contractions. Your uterus actually contracts throughout much of pregnancy, but you tend to feel it more towards the end. It may help to get plenty to drink and change your activity... if you were walking around and feeling them, go sit and relax for awhile for example. If you notice a pattern, start timing them. If you are before 37 weeks and you are getting more than 4 or 5 in an hour, and the increase in fluids, and changing activity doesn't cause them to subside, let your doctor or midwife know.

I'm 39 weeks. And they usually come when I sit. And then sometimes when I walk and then I have to stop but I don't know.

If they come and go, depending on what you are doing, they are likely braxton hicks. The real thing may start tonight, it may start in a couple of weeks... :)
If you start to notice more of them, start writing down how often you feel them. Had your midwife or doctor let you know when they would want you to call them? Often you will hear when the contractions are pretty regular, and not going away, to give them a heads up, but that doesn't mean you have to go in at that time. General rule of thumb for going in is when contractions are 3-5 minutes apart for at least an hour. We use the 4-1-1... 4 minutes apart, lasting 1 minute long, for 1 hour. Also will depend on how you are feeling, time of day, and how far away you live.
Hopefully not too much longer for you!