Dark brown blood is old blood that didn't have a chance to shed from uterine wall last period. Could be hormones. If your mom had hormone or female probs you will more than likely follow same path. Pelvic pain could be a number of things. Are you athletic, a runner, swimmer etc, Sometimes this can keep you from ovulating thus no period. Early meno? Don't know you need to get to a Gyno ASAP
best wishes
D
Because of your age, it is highly likely that your irregular menstrual cycle is due to hormonal changes. And that can go on for a very long time.
Although you have had a tubal, occasionally people can still get pregnant.
The dark brown blood could be signs of a miscarriage, or simply due to your hormones being out of balance.
Because it is uncertain what may be causing this irregular "bleed", I would suggest you make an appointment to see your doctor. I trust that you have kept a written record of your menstrual cycles and you can show this to your doctor when you see him.
The doctor can examine you and also arrange for a blood test to be taken to check your hormone and iron levels. He may consider sending you for an ultrasound scan to examine your ovaries and womb.
Keeping to a healthy and well balanced diet with lots of fresh fruit and veg, meat, fish and keeping off junk foods and foods that are processed (like white bread) and cutting down or avoiding foods that have lots of sugar in them, including avoiding fizzy drinks and too much alcohol can help with premenopausal symptoms. You may also find Evening Primrose oil helpful.
Do make an appointment to see your doctor and get checked out.
Let me know how you get on.
Best wishes.