If it's occurring more frequently, this may signify the presence of proteins in your urine, a condition known as 'proteinuria'. This can be related to a renal disorder or can be secondary to large quantities of proteins circulating in blood (as immunoglobulins).
Timing is an important aspect (whether it's transient, persistent or intermittent) and it's important to specify if this is related to a specific posture (upright position for example?)
I would advise you to visit a urologist and to do a urinalysis with a dipstick test to detect proteins in urine. Subsequently you may need to analyse urine collected for 24 hours to detect the amount and the type of protein present.