When can you have sex after ballon is placed in stomach?

Whenever you want...no restrictions. Just listen to your body. If you feel good, then it is alright and if you feel any discomfort lay low for a bit. 

It is generally recommended that you wait at least two weeks after having a gastric balloon placed before engaging in sexual activity. This is because the balloon takes some time to adjust to its new environment in the stomach, and there is a risk that it could be displaced or damaged if you have sex too soon.

Although there is no prohibition to have sexual relations after the gastric balloon placement, it is advisable to listen to your body, personally we recommend to patients who go through this, to wait at least 3 to 7 days before continuing with their sexual activity. The important thing in this case is to listen to your body and take into account the use of contraceptive methods during this period, since it is not recommended to have the balloon while you are pregnant.