You're bleeding between "periods" because you quit taking the pill. Anytime you do that (at the end of the pack or in the middle), you trigger your body to have some breakthrough or withdrawal bleeding since you stopped feeding your body hormones.
Birth control can cause a lot of the symptoms you were describing (nausea, constipation, diarrhea, moodiness, crying for no reason, nausea at certain smells, cravings, etc.).