The medication you were switched to, the generic form of Prozac, can take a while to work, up to six weeks in some people, even though the pharmacy companies often will cite best outcomes of 2-4 weeks.
Sometimes medications such as this, an SSRI medication, do not react well to individual biochemistry and may cause a variety of unexpected symptoms, including depressed mood. (rare but possible).
Although this is a straightforward answer, and I consulted with another professional on this as well, the best thing to have medication reevaluation. It does sound like something is not right and the emotional downturn could be the medication change or a reaction to your own unique biochemistry. In any case, you need to see you prescribing physician as these long periods of tearfulness are not normal. Steven