You definitely have a tendency to form stones and should be vigilant. It may be difficult to localise 4 mm stone if it is against bone shadows or preparation for the x-ray is not good. Ultrasound too is not very sensitive to identify stone from other artefacts. Your symptoms suggest that the stone has dropped down to either the lower end of the ureter or to the bladder. The symptoms you report are indicative of the same. The best course would be to just treat your symptoms with pain killers and you will pass the stone of your own. In any case you should consult a urologist who will advise you on what you should be done in the current state as well as how should you minimise the possible recurrence of the stone disease.