I think you should bring this up with your surgical team. I don’t think it’s “normal”.
I know exactly what you mean with your description as I had something similar straight after my op and for about 3 months afterwards, which severely limited my sitting (and, to a lesser extent, standing time). I’m pretty sure that my issue was mostly due to a large blood clot in the offending area which took a long time to disperse. My experience didn’t seem to be considered normal even just days to weeks after the op. It did gradually improve between 2 & 3 months. Even after 3 months I was using a haemorrhoid cushion if I had to sit for long periods though that was done by 4 months.
4.5 months seems long. Did you have any lymph glands removed? This can lead to localised fluid retention
Nick