Hello and welcome to HCM,
Unprotected sex 11 days after last menstrual cycle can coincide with ovulation.
Ovulation takes place 14 days after last menstrual cycle in a 28 day cycle.
Since, the menstrual cycles vary in their duration, so the exact day of ovulation can vary.
You need to take up a
pregnancy test.
Lower
back pain can also occur due to transmission of sexually transmitted diseases (STDs).
Since, you had unprotected sex, there is possibility of transmission of STD.
STDs are characterized by discharge, ulcer,
rash,
lymph node enlargement, itching, or vesicles on the genitalia.
If any of these symptoms are present you need to consult your gynecologist for clinical examination.
Breast tenderness is progesteronal effect.
Progesterone causes retention of water and thus, breast fullness and tenderness.
Pregnancy test is the first thing to be done.
Thanks and take care
Dr Shailja P Wahal