Ema,
You may not need to replace the gauge. Try removing it an cleaning out the hole in the bottom. Because the gauge is before filtering, they sometimes will get clogged.
Second, I took your original post to mean your pressure reading was near 0 PSI which would be impossible if you had any flow at all and would indicate a problem with your gauge. However, if your return flow is significantly lower than before, and your pressure gauge reads equally lower (but not 0), it could indeed be suction side blockage and worthwhile to check out.
Most of the posts I have seen on other forums regarding low PSI have turned out to be a problem with the gauge.