Had a bad headache, running nose and cough last week. those symptoms are over but for 2 days yellow mucus with blood. what could this be?

Resid inflammation: Most likely you have some minor residual inflammation left over form your viral/allergy medicated cold you had last week, that shows as pinkish tinged mucus. Stay well hydrated and if that does resolve soon, see the dr. Best wishes.

Residual infection: If does not improve in a few days see your doctor to check for a sinus infection. You can try a saline nose spray to clear out the nose.