Actually since you had your tubes tied, you cannot possibly be pregnant because it is by far the most effective mode of contraception. However, from where I see it, you might be heading towards Menopause. Menopause is often characterized by irregular periods, Nausea, and tender breasts, amongst several other symptoms. So I would recommend you to consult a doctor as soon as possible. Here is a link to a website for more information on Menopause:
www.project-aware.org
www.project-aware.org