Lots of things can cause the symptoms you are describing - anything from appendicitis, to gastritis, to acid problems.
f you are concerned then go to A&E. If they suspect gallstones they will simply do an ultrasound check of your gallbladder - it's really easy to see them. They will also do blood tests to see if there is a blockage that is causing a backup of bile to your liver, or an infection caused by inflammation. It'll be pretty obvious if there is a blockage: it makes the liver go bonkers and the tests show big time readings if the blockage is bad enough.
In my experience the worst attack was after eating (depending on the contents of the meal - anything fatty will really cause a conniption). I'd end up in the foetal position...even puking wouldn't help, and there is no way to "stop" the pain (unlike, for example, bad gas or acid - which can be helped with gaviscon or other treatments like sleeping with an elevated pillow etc).
The pain is in the right side - not the left. And often with bad attacks will refer pain up into the right shoulder/shoulder blade area because there is a nerve that is impacted by the gallbladder/liver that runs up into that area. You'll also experience pain in that area if you end up having the gallbladder removed by keyhole surgery: there will be residual CO2 in your abdominal cavity that will cause pressure on that same nerve - and it'll cause pain up in the shoulder/collar bone area. It's weird but hey, that's anatomy for you.
In addition to pain you may also find that you are dizzy/feel very woozy - this happens even more if your liver is being damaged by the blocked bile duct. The docs initially diagnosed me by pushing on my abdomen - which caused immediate dizziness/feeling like I was about to pass out. Add that to the other symptoms and I was immediately rushed to the A&E. My liver tests were off the charts bad because of the damage that the blockage was causing (a basic way to think about it is that bile is supposed to help break down fat - but if it backs up into the liver it starts digesting the liver instead - not good!).
If you have any kind of gallbladder inflammation or liver damage caused by gallstones then the appropriate treatment is to have the thing removed. Unless you have issues that prevent surgery or make surgery more difficult (being obese for example). Note that many people have gallstones and/or gallstone "sludge" - the big stones aren't actually that problematic as they just stay in the gallbladder - it's the little ones that block the bile ducts that are the worrisome ones. In my case I had a couple of pretty big stones and a bunch of sludge. If you have the gallbladder removed they will typically send bigger stones away for biopsy just in case there's something problematic about them.
If you want to lessen your symptoms in between now and getting treatment then change your diet. You can find information on this on the NHS website. Gallbladder contractions are prompted by fatty/rich food, and also by eating too much food. Eat healthy food in small portions, and be sure to drink enough water.
As for painkillers: no over the counter painkillers will control the pain caused by a blocked bile duct. It's a pain that really only IV hard core pain meds can tackle - and even then...