Do what you feel is ok with you, but I would personally stay away from aerobics because of the dizzy spells and the fact you are not having many calories.
Do some toning and walking, etc...light exercise to help tone up.
I have a health club membership and usually do coreball, pilates and yoga, although not been since before Christmas due to the snow! But, I will be taking it slowly as I dont want to keel over or feel unwell as I know I am putting my body through enough.
Whatever you do, you will know what is too much for you.