Maybe the meditation is like the medication - if you end up feeling sad you probably won't want to keep it up, so try adjusting the dosage. I don't know how much time you spend meditating, but even if you have to cut it down to literally one minute (and do it a few times during the day) to avoid feeling sad that is still better than dropping it entirely. If in your mind you start to associate feeling sad with meditation, it will change how you feel about meditation. That can be worse than not meditating at all. I think that if you are patient with yourself you can get past the sadness and learn to enjoy meditation so that when you stop you still want more.