that's not nice

1 cup fresh lemon juice
1 cup warm water
1 cup white sugar

mix thoroughly
put in juice jug & add cold water in increments till desired taste is reached.
failsafe method I've been using for ages. You can adjust easily for bitter/sweet as you go.

I think people have been giving good advice. If the sugar doesnt dissolve proprely, it wont taste sweet. Try using warm water to dissolve the sugar first, when the water is sweet, add lemon juice till it tastes good. Also, wash your lemons thoroughly before squeezing them, chemicals on the peel could impart a bad flavor to the lemonade..

I like mint leaves in my lemonade

You can get them at almost any supermarket