It really isn't recommended to take any EO internally because of their strength. If you are wanting to make something to ease stomach ailments etc you are far better off making a tea with the herbs, or even your own tincture using the herbs.
Try this experiment. Take a styrofoam plate, or whatever and put 1 drop of Spearmint Essential Oil on it. Watch what happens. Within seconds the styrofoam is melting. Do you really want to take that internally? That's why it is sooooo important that EO's not be applied neat but rather diluted into a carrier oil.
Lemon juice is easily accessed and far less expensive. For lavender, buy lavender and make a tea, same with the mints. You'll be far happier and safer with the results.
Just saying....