Hello dear, Thanks for being on healthcaremagic.com.If you would have presented to me as an outpatient,I would have made the following clinical explanation- Pulsatile headache otherwise is said to be classical for migraine but here the headache is not episodic,it is rather constant and progressive in nature for past 2-3 months.It is localised on left side,and that makes it a red flag.I say it here a red flag because though migraine is also unilateral pulsatile headache but here the headache is progressive unlike migraine which is usually episodic.A progressive localised headache must be evaluated by a brain imaging study like computerised tomographic(CT) scan for structural abnormality like a space occupying lesion in brain.So,please discuss with a neurologist and get a brain imaging study done.I hope it helps.