Every time I have a tea with lemongrass in it the tea ends up with a really strong and rather terrible aftertaste. I drink several different types of tea, and am pretty sure that I am letting the lemongrass steep for too long. What is the optimal time to let lemon grass steep? I typically start with my water at 100 degrees Celsius.
I assume that you're making a cup of black (?) tea and steeping some lemongrass in it. If so, perhaps you should make the black tea very weak as its tannins might be amplifying the (pleasant) slight bitterness of the lemongrass to distasteful levels.
Alternatively, if you are steeping the lemongrass in hot water, try removing the outer layers of the lemongrass stalk. If they are old or tough, this can increase the bitterness of the drink.
In any case, check that there isn't any dirt trapped between the layers of the lemongrass.
Some recipies call for putting the lemongrass into water, bringing it to a boil and then letting it simmer for 10-15 minutes. I haven't tried this. Even if it does produce a smoother taste, then the boiling might well degradge any health-giving nutrients from the lemongrass.