An alternate explanation for what you are experiencing is that the reason you find it difficult to pee is because there is very little urine in your bladder and you don't actually need to do so. Prostate surgery leaves the bladder neck irritated and inflamed and the feeling of having to go even if the bladder is nearly empty can be pretty compelling. It's hard to develop a decent stream if you only have half and ounce to work with.
That was my experience. 3 days after the cath was out I made a terrified call to the uro on call at midnight feeling like I was in retention. I was dressed ready to hop in the car to the ER. After some questioning he had me drink some water and walk around for 15 minutes and call him back if I hadn't gone yet. It worked, my bladder must have just been empty and with a little more back-pressure I was able to pee.
Hopefully that's all it is and things will improve for you quickly.
Age at Dx 54 10/23/14 PSA 9.75 DRE- T1c
Biopsy: 2 of 12 GS7 (3+4) 7% of sample #1=20%G6, #2=10%G7
Scans: 1/22/15 CT / Bone Clear
DaVinci: 1/27/15 Prostate 36gr GS7 (4+3) 8% of organ
PNI+ EPE- SV- LN- Clear Margins pT2c
uPSA Post Surgery Every 3 Months <.05 <.05 .03 .03 .05 .07 .09
6 mon Lupron @22 months post surgery PSA .09
Then @24 months SRT (25) 2.5gy = 62.5 gy Hypofractioned Tomotherapy