I had the synvisc injections too!
had the 4 times (3 inj. each) yes they do help by replacing the cartlidge BUT they onlt last about 6 months so you are a little short of the time but everyone is different.
talk to the doc and tell him the pain is returning, if the inj. was in Jan. then you need to wait till August

sorry I can't give you better time frame, also the weather and your life style play's a big part too. I hope you aren't wearing the high heal shoes again, they are really bad for your knees
hope you are feeling a little better
As for me, I am looking at knee replacement later this year
ken