I agree with Vidalia on this one. Smoking pot will not make you happy. In fact it has been linked with long term depression. How long have you been smoking? If it is a long time it may be contributing to your low mood.
Low mood can be tackled very effectively using nutritional means. Self-medicating with marijuana will only make it worse.
There are powerful (and legal) mood boosting compounds available from any good herbal retailer.