Thank you for your query at DoctorSpring.com
I understand your concern.
It is not possible to have a lumpy feeling secondary to trapped gas in the tummy. Mostly because all the gas is trapped inside the intestine till it comes out, and the intestine is a very big organ, so such lumps due to gas can't be felt.
The stomach only appears a little distended following a heavy meal, and that is more of a generalised feeling of fullness. There is no such particular spot, which gets distended even in this case.
So in order to find out what this lump exactly is, I will advise you to get an Ultrasound whole abdomen done, which can explain the origin of the lump. Please do not worry as this does not likely to be anything serious in absence of any other symptoms.
Feel free to discuss further,