hmm...I would talk to a doctor about it. Any time you have unusual secretions, you should talk to your doc.
When you're fertile, you discharge a sort-of egg white looking secretion. Is this different than that? It sounds like that may be what it is...especially if the secretions only happen once a month. If they're more spread out and sporadic, then it's not fertility.
But yeah...talk to your doctor about it.