Could Light Pink Blood Discharge Between Periods Indicate Pregnancy?

I was wearing a panty liner and when I went to go pee I realized that there was light pink blood/discharge on it. I have never had this happen in my life and I shouldn t be getting my period any time soon. Last time I had sex was on March 7-March 8. I did get my period after that but is there a possibility where I could be pregnant? Or can it be an STD??