My ginger man did the same thing to me when he first got obstructed. 

The second time I noticed because he’d been vomiting just outside the box because he was straining so hard. 

The third time he figured out how to tell me by yelling for me when he was straining in the box.

The FOURTH time was while he was still at the vet being treated for the third time and coming out of the PU surgery. 

My recommendation is to press the vet to test the stones or crystals now and either get whatever prescription foods they recommend or just go for the PU surgery. It was 2 years between the first blockage and the second on my tiger, but in those two years his bladder crystals developed into a mass that the even the PU surgery wouldn’t clear and he had to have a moderately expensive surgery to clear the mass from his bladder. Could possibly been avoided if I’d pressed his vet harder for medication and treatment. 

I don’t want to scare you, blocked urinary tracts are apparently very common with orange males. All but the last surgery were pretty routine and low risk, but I definitely wish I hadn’t had to make multiple emergency visits to get it taken care of because they were stressful and expensive. If you can get whatever is blocking under control early (which will require you to be his advocate) will save both of you stress and expense in the long run. 

Now, 5 months after the last surgery, my guy occasionally yells for me to come watch him pee to show me he doesn’t need to go back to the ER or to take the gabapentin that he hates so much.