Why are two echo report different?

I had an echo done in an outpatient hospital secondary for a weak heart murmur. I 'm age 31, the only symptoms are I always feel dehyrated and hypotensive, especially in morning even though I drink >3L of fluid/day, I also feel shortness of breath during intense exercise(i.e. run about 1 lap or swim freestyle for 1 lap, I can jog or swim breast stroke with no problem). I found that my strength and endurance of exercise is less compared to peer of my age. The first echo showed mild increase in right-sided heart structures with mild elevation of right-sided pressure( right ventricular systolic pressure of 34mmHg) and dilated inferior vena cava. There is also an atrial septal aneurysm with a righ -to -left shunt demonstrate on bubble study without valsalva.
Three weeks later, the doctor repeated an echo at his office and he told me that everything is normal. He said I had a PFO but that is not to be concerned about, the shunt is just from the weakened membrane(aneurysm). There is no enlarged right heart or elevated pressure and no dilated inferior vena cava for this second echo.
My questions are:
1) Why are the two report so different? I don't have any change in my clinical condition during this time. What factors can affect the report results?
2) What is the difference between atrial septal aneurysm and PFO? Are they the same thing?
3) Why is it right to left shunt and not left to right shunt?
4) What is the implication or consequence of this?
Thank you so much!
lucy