The following information is what happened to me personally, but I am not a doctor by any means.
With my obstruction I was severely constipated for months. Also the pain got more and more severe. When it became blocked I was on the floor in excruciating pain for up to 30 minutes at a time. I finally went to the ER after puking and the puke became extremely painful, hot like fire, and also it had been a couple days since having a bowel movement.
A lot of the time I would be in a ton of pain and I could basically feel like the food was struggling to get through the narrowed area. Once it got through the narrowed part of my intestines, my stomach would make a gurgling gassy noise and the pain would subside, only to begin again within a matter of sometimes just ten seconds.
If your pain is excruciating, go to the ER. If you have a steady throbbing or pulsating pain for days on end, go to the ER. Don't make the mistake I did by dealing with it (toughing it out for too long) and ending up having to get surgery. You want to avoid that. Obstructions are very dangerous. At the very least you can get pain relief from the ER. They will also get you a CT scan and blood work and you get to find out the results quickly. From their they will know what to do.