Are you using a skin barrier/prep? Sometimes that helps. What are you using to clean your skin? You may have oily skin, I always use a deoderant/antibacterial soap which strips your skin of oils.
Are you using any powders or creams that could prevent it from sticking?
The other thing would be that it's the wrong size opening. Is it pre-cut? You may want to try bigger, if you're cutting it, try cutting a little bigger.
Does your stoma protrude evenly all around, or is it flat and/or flush with your skin?
Do you do strenuos activities? Sweat a lot? Do you let it get too full, or full of air? Sorry, more questions than answers.
It may be as simple as you need a different type of pouch. You may want to ask your doctor for an ET nurse to come out and help you figure this out.
You should also be able to call your supplier and tell them you've had an emergency and that you need more supplies. They should be able to help you even if it's to just send samples. This is also why you should always have an Rx on file signed by your doctor for a large amount of supplies in a month's period.