I had a colonoscopy this morning. i weight 134 when i left my house. i just weight again this evening, i am at 138. is this due to the gas from the colonoscopy?

Body weight tends to fluctuate throughout the day and sometimes between days due to fluid shifts as well as as food intake and bowel movements, and less likely due to procedural effects. Especially for those monitoring their weight or actively managing weight goals, it is best advised to weigh oneself at the same time everyday to track weight, ideally in the morning naked

The difference in weight is not likely to be from gas given during the procedure. Part of it may be that you were somewhat dehydrated from the preparation and that you received IV fluids and drank fluids to help catch up. You should notice that it stabilizes over the next day or two. Good luck.