Wats the pecentages of a false positive pregancy test took one test it was positive took another it was negative 4 months laters IV gained weight but I've also stoped smoking

Not sure I get it. You had a positive pregnancy test, but you did not go to see a doctor, and you waited 4 months to get another test? False positive tests vary by the kit you are using, but they are uncommon. You need to see your health care provider for a more definitive test. If you get a positive test in the future, you must see your health care provider asap to confirm diagnosis and care for the pregnancy.
Lots. Lots of possibilities: (1) you were indeed pregnant. Your pregnancy progressed to some point and then stopped. You haven't "passed" the pregnancy yet-- as in a miscarriage. Ultrasound is a good test to get to the bottom of this. (2) you were never pregnant. You had a false-positive test. This happens in a small fraction of women. (3) you're still pregnant, and have a false-negative test. Take another test. Thanks for quitting smoking!