You may just need to wait a bit longer to see results.
If that's not the case, then you may just need to bring your energy up.
Little tricks like meditating, writing a spell out in a foreign language, singing, etc, are helpful. Sometimes spells with intense emotion attached get results quicker.
Doing a spell more than once isn't a bad suggestion, but you run the risk of putting out a 'doubtful' energy; actively working against your own spell.