Why does only some weird food gives me tooth ache (dull, not sharp) when chewing them - like pickled garlic?! (not sweet)

Acidity: It is possible that the acidity of the pickling solution is irritating a broken tooth, a loose filling, or a cavity. Either way, have yourself examined by a dentist. Minor problems can be easily restored with a simple, inexpensive filling. Let it go, and you will spend 20x as much for root canal therapy, post, and crown. All the best...

Cracked tooth?: That could be cracked tooth. X-ray and a local exam would need to be performed to give you an accurate diagnosis. It could be so many other reasons like opened margins in an existing filling, the best for you would be to visit your dentist and let him to look at the tooth.