Why not go Udon Thani from vientane and book a ticket on the spot. Udon has like 5 different companies flying to BKK every day and cheap.2 hr bus ride.
time to extend some more and spend some time at a temple. After come back to FB and try to be a bit more helpful instead of calling people stupid. Thank me later.
If u arrive at Suvarnabhumi you can go to the basement where you can find city line train connected to BTS. They have a taxi office at a different floor. Dunno if grab is accepted inside airport. At basement they also offer good money exchange office.