Amber,
I work night shifts, I am a nurse, hence the early AM reply. Sorry to hear about all your concussions. That Laundry is a dangerous place and when you have had past concussions, it does not take much to cause injury and symptoms. Most PCS patients have normal scans, so you might be alright not scanning. Laying low and resting is what is reccomended, which I am sure you know. The pressure in back of head does not sound kike sinus issue. Take it easy and hopefully the pressure will stop with rest. You may not have PCS if that is your only symptom. Do you have dizziness, memory issues fogginess or personality changes? Hang in there and hope things improve soon.