I found that while germinating very fine seeds like catnip I had to keep the top of the soil fairly moist since the seeds are not planted very deeply and the surface dries out so fast. A walmart sack or cut translucent plastic set on top of the seed starting area helped retain moisture while waiting for germination so I did not have to mist the soil twice a day. It took my cat nip at least 14 days to germinate.
Same with lemon balm, basil and most plants in that mint family (Lamiaceae http://en.wikipedia.org/wiki/Lamiaceae) very fine seeded and shallow requiring more care to maintain moisture.
Anyhow, keep em moist, horticulture is a test of patience and good luck.