I'm sorry to hear about your little pug guy. There can be 1 of 2 things happening with your guy.
1. If he is squatting and trying to urinate frequently, he may have a bladder infection/inflammation, and he may be going very small amounts frequently. In this case, any time there is a little urine inthe bladder, they feel like they have to go and strain against an empty bladder. In this case, a urine sample and antibiotics are necessary.
2. The second, and more dangerous, situation is that his urethra could be blocked and he is unable to urinate. In this case, he has a full bladder, but can't urinate, and so the urine backs up to the kidneys and causes all kinds of problems. The blockage could be due to bladder stones or a urethral or prostate mass. In most cases, a veterinarian would be able to feel a hard and enlarged bladder which can't be expressed. Xrays ca pick up most bladder stones. If xrays don't show a stone, a urinary catheter can be passed 1. to allow urine out, and 2. to feel for grit, obstruction, etc. Sometimes ultrasound or dye in the bladder can give a more definitive diagnosis.
If it is the first problem, you should see your veterinarian, but it is not life threatening. If it is the second problem, that can be life threatening, and you should seek veterinary care immediately.
Here are some links that can tell you a little more about urinary obstructions:
Hope this helps. If there are any further questions, please reply and I'll get back to you as soon as possible.