I would definitely go to see your primary care doctor
or your OB GYN doctor about this issue as soon as possible. It sounds like you are suffering from galactorrhea, which is lactation in the absence of childbirth and breastfeeding. There are a number of medical conditions that can cause galactorrhea, and your doctor will want to evaluate you for these conditions. Many of the medical conditions that cause galactorrhea will also cause menstrual irregularities, which it sounds like you may have as you have been checking to see if you are pregnant.
For example, hypothyroidism is a condition in which the thyroid gland does not produce enough thyroid hormone. In addition to a lot of nonspecific symptoms, such as fatigue or weight gain, hypothyroidism can also cause galactorrhea.
Similarly, a small growth inside the pituitary gland may produce an excess of a hormone called prolactin. Excess levels of prolactin will cause galactorrhea and will most of the time also cause disruption in the menstrual cycle.
Both hypothyroidism and prolactinemia (elevated prolactin levels) can be checked by your doctor with basic blood tests.
Finally, there are a few classes of medications that can produce galactorrhea as a side effect, and your doctor will want to review any medications you are taking to rule this out. Please make an appointment soon.