Try fitting the fuel cap loosely (or remove it) when the tank is full.
If the car runs okay - that points towards a vacuum problem with the tank.
A fuel tank would normally have a vent to atmosphere via a tube which will be somewhere around one of the wheels, or a rubber valve in the fuel cap itself.
Other than that, a warning light associated with emissions/poor running usually comes down to the O2 -lambda - sensor, which is fitted in front of or on the catalytic converter. Ideally, you'll need somebody to connect a diagnostic scanner and read the error code generated by the warning light. Once you know the error code - that'll point you in the direction of the real cause of the problem.