Pack on scar brings pain

Two days ago, I decided to use a castor oil pack on my tummy for the second time since undergoing laporoscopic myomectomy three weeks ago. Out of the 3 incisions, 2 were fine right from the beginning but 1 of them may have been slighly infected, anyway the slight rubberish scab/pus on the surface came off several days ago. There were never other symptoms of possible infection.

I used a Heritage cotton fennel that was used for the pack one week before, laid a piece of clingwrap over the fannel and out my hot water bottle over it. The strange thing is that although the water bottle was quite hot, it felt fine on my tummy except for that problematic incision, which felt a little painful, as though it was being pinched.

Is that supposed to be normal? I did not experience such pain last week, but I did put a little more castor oil over that area this time. Could it be that the oil was working its way into that area and healing the scar or internal adhesions?

Hope to read your thoughts about this. TIA.