Most medications do not prevent you from donating blood. Common medications such as those used to control blood pressure, birth control pills and over-the-counter medications do not affect your eligibility. If you have recently taken antibiotics, you must have completed the course prior to donating.
Yes, a tooth infection can cause a headache. Also, be aware that certain sinus conditions can mask as tooth problems.
Sometimes a tooth infection can cause supraeruption of that tooth, placing the cusps in harms way. The ensuing symptoms will be a part of the Sprained Tooth Syndrome but secondarily to the tooth infection. Again underscoring the need to find out why a tooth has moved into this damaging position.