Thanks for your query.
First of all you need to do a urine pregnancy
test to rule out pregnancy as you have had regular periods and never missed them.
Secondly breast tenderness is also one of the symptom of pregnancy.
If urine pregnancy test is negative then your spotting is due to hormonal
And if the test is positive then it will be due to threatened abortion
I would suggest you to get urine tested for pregnancy then consult a Gynaecologist and she will do the needful for you.
Hope this answer is helpful to you.