Range of Motion restricted 6 months post op

Hi all, was doing absolutely incredibly during my recovery (I ran a Marathon at month 5 if that gives you any context). After a workout at the gym (I’m at 6 months post op), I woke up today and found my knee really sore and my range of motion restricted compared to my good leg, back to where it felt a month from op. I think this is workout related as I can feel the soreness through my hip. I was at my computer for an hour today and upon standing I had trouble walking. Is this anything to be worried about? Do I just need to ice and rest, or do I need to see my surgeon and/or PT again? (PT let me loose after I successfully ran the marathon and just told me to do the exercises at my gym)