Flat beer in bottles

[Crichards1975]

Can I add sugar to my 1 liter plastic bottles of an American amber ale? They are barely carbonated and borderline flat. They have been maturing in bottles for about 4 weeks mow at room temp. Any advice? Should I add sugar or just poor them on my buddies keg and co2 that 5 gallons?

 

[MalFet]

Did you add sugar when you bottled originally? Why didn't they carbonate?