After 2 weeks of eye strain, poor neck posture and tension a pulsating(visibly beating) vein (or artery) on my left temple popped up and been appearing and disapearing since then (3 days). should i be concerned or just relax for a few weeks?

I would suggest that you need a proper medical workup to include bloodwork to exclude serious autoimmune problems such as Temporal Arteritis which would be unusual at your age or other rheumatologic conditions. This condition merits immediate treatment as ignoring it could result in blindness. More likely than not this is not the problem but you would not want to miss the opportunity to treat

Try optometry for new glasses to reduce eye strain and check your blood pressure for the engorged vein. Temporal arteritis in a 30-year-old would be very unusual. Try to improve your ergonomics for better posture. Get checked for Lyme disease.

FIRST, do not worry about temporal or giant cell arteritis, as "vein (or artery) does NOT come and go over several days, and rare in your age group. Perhaps the core issue is neck strain, and important to address this, as this likely explains everything! Some physical therapy may reverse all of this. Yes, get eyes refracted to cover bases. Have your doctor do exam and proceed.