Yeah, you should have definitely have a lithium test done, as like hexagram quoted lithium is only effective at a certain level, so blood tests are needed quite often in the beginning.

Usually when you first start on lithium, it is a pretty low dose to see what your body does and a test should follow to determine how your dosage should be raised. This is because everyone gets to the therapeutic levels with a difference dosage. For me, I need 1000mg to even hit therapeutic, but I know someone who takes a bit less.

You also need to make sure that you get your thyroid tested periodically as well after you get to a therapeutic level, because lithium can damage it as well.