I m a US citizen and at bkk now, flying back to US do i need a visa?

I m flying back to US via BKK(7:10pm)>PVG(12:45am)leaving 6:50am>TAO(8:30am) leaving 1:15 pm> SFO
I was told by China Eastern Air that I need to get Visa in advance since i m flying to different airport.
Is this correct can u confirm soon since i m flying in thex next 5 days.
Thx