The flowers look like Nepeta cataria, catnip, but the leaves make me wonder if it's something else. I think that the different lowest petal size and markings rules out Mentha arvensis, is that right?
Thank you, @Tyrlych! I didn't even know that word. Lycopus europaeus is European horehound (gypsywort), seems most similar of the Lycopus likely to be found around here.
