Cellulitis-red lines on skin

about 2 and a half hours ago I noticed an inch long thin red line in the middle of my inner arm, almost like someone marked my arm with a red pen. Thirty minutes ago a longer red line appeared near my wrist–about three and a half inches long. It also appears to be almost perfectly lined up with the mark in the middle of my arm, which is still as red as it was two and a half hours ago, although it hasn’t gotten longer(unless the new mark is an extension.) I just went to a doctor and he said it is hives from a scratch. Then he scratched my arm with a pen to show me. but the scratch marks from the pen look thicker and several shades lighter than the original lines, and I’m about 95% sure I didn’t scratch my arm while it was resting on a table.

I can totally accept the idea that I’m freaking out and I should trust a doctor’s opinion, since the past two months I’ve had extreme hypochondria about septicemia/blood poisoning/cellulitis, butI just can’t understand how I would completely forget scratching my self not once, but twice. And the fact that a scratch looks fairly different from the two lines.

My girlfriend is angry at me now because she thinks I’m overreacting, but I also know that unexplained red streaks on your body shouldn’t be taken lightly, since blood poisoning is serious business.

Should I get a second opinion? Any other signs I should look for.

Check with more docs, the other thing it might be is shingles, but just go to a big hospital to check.