Period once in the last 4 months. Stomach discomfort, negative HPT. Changed birth control 3 months ago. General yucky feeling. Possible conditions?

Irregular periods. Irregular periods are one of the most common problems obgyns treat. If this is one time problem it usually resolves on its own. If this is a recurring problem you should be evaluated. Infections & hormonal changes can cause spotting. If there is a concern for pregnancy then do a home pregnancy test . There are many options available to help regulate the menstrual cycle. Schedule a visit.
Hormonal imbalance. You may be entering menopause and should consult your doctor for an evaluation. Menstrual irregularities are not uncommon and anovulatory cycle is a common cause. Consult this site for more information on this topic.