It's not just you, and it's not just level 30. Merle has started telling me this time I level up and always says the same thing. You might want to look just in case, but it's usually nothing. There is a topic about this in the FAQ. The title is 'Merle Summoned me, but has nothing for me!' Fiona Mythsinger, Level 53 Pyromancer
First off, remember to check the FAQ. Second, this is a random glitch that annoys so many players. It seems to happen less now though. However, you should check, as Merle will sometimes have important quests for you!