I agree with Mark, that doubt can affect the flow of energy from the crystals. When you are fully open to receiving the energy it is much more effective.
Think of the flow of energy like water flowing from a pipe, if you clamp down on the middle of the pipe, only a little water will flow, restricting the output. You'll still feel the effects, but it has been dampened, and healing will can take longer.
I believe the same goes for any healing modality however, your state of mind has much to do with how fast you recover, even with modern medicine.
It is normal to have doubts and they are not always the easiest things to let go of. Don't force yourself, but work on opening your heart and mind to the energy. Meditation works well, but if you have problems with that, sleep with the crystals. You mind is much more open at this point.
Cleanse your crystals often too, selenite is a quick and easy way to cleanse and charge your stones. Just place them on a chunk, then you don't have to worry about reaction of sunlight or with water.
Good luck with your journeys.
