I had my af on the 7th feb. i'm now 3 days late and experiencing back ache headache, feel tired & constipated could i be pregnant did a hpt but neg?

Take a test: Sometimes the two go together or they can be random, but they are not typical symptoms of pregnancy. Your headaches could be coming from tension, dehydration, lack of sleep/poor sleep, skipping meals, stress, teeth grinding, sleep apnea/snoring, or chronic sinus problems among other things. See a doctor to get checked out so you can get some help for your headaches.