Thanks for the query.
As you undergone tubal ligation
and as the blood test
for pregnancy gave negative result, the possibility of pregnancy is less.
The spotting and the symptoms you are having could be due to hormonal imbalance.
The other possibilities are:
-Thyroid hormonal abnormality
-Pelvic inflammatory disease
- Gastritis etc.
Discuss these possibilities with your doctor advice
, if she recommends go for thyroid profile and ultrasound
Then depending on the reports you can go for the treatment.
In case of hormonal imbalance, hormonal pills for few months, can help in regularization of the cycles.