Clematis most  often fail to bloom due to being too young, too much shade or cold weather. If you have a white clematis, it could be clematis armandi with narrow, lance shaped leaves that are mostly evergreen. This clematis flowers in early spring so because you are writing to me in March about no blooms my hunch is you have the early flowering clematis. For these early bloomers a late frost or cold wind exposure can stop the formation of buds thus no blooms. The early bloomers do best in a very protected location out of the wind.  You may want to transplant your disappointing clematis to a new location and replace it with the later flowering varieties such as clematis Jackmani and Nelly Moser as these clematis are more weather tolerant. Keep growing, Marianne Binetti