A lot of people on here have suggested that you get a blood test. I would follow this advice. Also, most women who have had a tubal ligation and find that they are pregnant end up finding out the pregnancy is ectopic.
Another thing you might consider is a condition called post tubal ligation syndrome. Most doctors either know nothing about this condition or don't know enough to advise their patients about it when considering tubal ligation. I had a tubal and am now living with chronic fatigue, early menopause symptoms and every time I ovulate or menstruate I have crippling migraines. I am only 31 years old. Here are some of the symptoms that can occur and a link to a website that gives more information about the condition.
SYMPTOMS OF POST TUBAL SYNDROME
1. Eptopic pregnancy or pregnancy (well known risk of tubals)
2. Hot flashes, flushes, night sweats and/or cold flashes,
clammy feeling, chills
3. Bouts of rapid heart beat
4. Irritability
5. Mood swings, sudden tears
6. Trouble sleeping through the night (with or without night sweats)
7. Irregular periods; shorter, lighter periods; heavier periods, flooding;
phantom periods, shorter cycles, longer cycles
8. Loss of libido (see note)
9. Dry vagina (see note)
10. Itchy vagina-at time raw like, can radiated from whole area, with
absence of yeast infections. (see note)
11. Color change in vaginal area. (color gets darker -darker red to purple)
12. Crashing fatigue - Chronic Fatigue
13. Anxiety, feeling ill at ease
14. Feelings of dread, apprehension, doom (see note)
15. Difficulty concentrating, disorientation, mental confusion
16. Disturbing memory lapses
17. Incontinence, especially upon sneezing, laughing; urge incontinence
(see note)
18. Prolapse of uterus due to rapid decrease in estrogen levels.
19. Itchy, crawly skin (see note)
20. Aching, sore joints, muscles and tendons (see note)
21. Increased tension in muscles
22. Breast tenderness
23. Decrease in breast mass
24. Headache change: increase or decrease
25. Gastrointestinal distress, indigestion, flatulence, gas pain, nausea
Irritable bowel syndrome (IBS)
26. Sudden bouts of bloat
27. Depression (see note)
28. Exacerbation of existing conditions
29. Allergies developing or increasing - (Chronic sinusitis).
30 Nasal infections-necessitating antibiotics
31. Weight gain (see note)
32. Hair loss or thinning, head, pubic, or whole body; increase in facial hair
33. Dizziness, light-headedness, episodes of loss of balance
34. Changes in body odor
35. Electric shock or stabbing sensation under the skin. (see note)
36. Tingling in the extremities, (see note)
37. Gum problems, increased bleeding
38. Burning tongue, burning roof of mouth, bad taste in mouth, change in
breath odor (see notes)
39. Osteoporosis (after several years )
40. Changes in fingernails: softer, crack or break easier
41. Stabbing pains in pelvic area at time of ovulation
42. Pelvic Pain
43. Development of Adenomyosis
44. Development of Ovarian/Tubal Cysts
45. Decreased Lactation Ability
http://www.tubal.org/symptoms_of_pts.htm