Hi, I Have Been Experiencing Slight Discomfort In My Left

hi, i have been experiencing slight discomfort in my left chest which initially felt like a little lump. it has been ongoing for 1 and a half week. this litle lump slowly became a thin cord which looked like a potruding vein showing on the left chest. this runs from the bottom of the left breast all the way down to the mid ribcage. i have been to the GP when the pain was there and he dismissed it as a muscle pull. should i be worried about this condition? or should i just leave it on its own.