Thanks for the query.
In fully breast feeding women periods can get delayed due to the effect of the hormones.
And if you had unprotected intercourse
during this time there is possibility of pregnancy
Sometimes urine pregnancy test kits may not detect early pregnancy.
So better to go for blood test
for pregnancy once.
If the test comes negative, the possibility of pregnancy is very less.
And the symptoms you are having could be due to premenstrual hormonal
effect or there is possibility of occurrence of ovulation.
So if the symptoms persist, consult gynecologist once.
Get examined to find out the exact cause and take symptomatic treatment.