This is a problem that has been with me since ever I could remember. I used to think people were lying to me when they say that apples and watermelon is sweet. I thought that they are just making me eat it because they are healthy. It took me a while to realise that they are speaking the truth and that I was the one with the problem. 

I cannot taste the sweetness of a lot of fruits, eg. apples, watermelon, pear, strawberry, cherry, papayas. These examples are the ones I have actually tried. So this means that if you blindfold me and fed me an apple and a pear, I wouldn't know the difference. One encounter with strawberry is that I took a bite out this nice looking strawberry, it only tasted sour to me. However, when I pass this same strawberry to my mother, she informed me that it is in fact, extremely sweet. 

The fruits that I could actually taste, are described to me as the "sweeter fruits", such as bananas, mangos, longans, lychees. 

Another condition I have, although not that serious to my daily life, is that I have a slightly inferior ability to differentiate between sweet and salty. Example would be that I would take quite a long while if you pass me containers of salt and sugar and ask me to differentiate between the two. 

So, is this common?