It would have been much more useful had you supplied more information about your wheel than just the number of spokes. The type of hub you have is important in diagnosing the problem. It is very frustrating for people giving answers to not know what they are dealing with. The make and model of your bike would be a help. If your bike has a freewheel, your hubs may not be up to supporting your weight, if you have a cassette hub, the problem could be something else.