Give it at least a week, rest and ice, gentle physio type exercises. Presumably the knee is arthritic and was painful before the injection. The HA injections can take 6-12 weeks to take effect
The single jabs are more painful apparently as the substance is more viscous that the multiples. My surgeon no longer uses the single ones due to greater pain (his preferred brand is Ostenil, assume you are in North America where Synvisc/Monovisc seems more used).
Good luck