Could my pain be from sacroiliitis?

I have psoriasis and psoriatic arthritis. I have had PsA for at least 25 years, but only diagnosed about 4 years ago. I have always had some back pain but it has become worse of the last couple years. I have read about some of the things that can cause this kind of pain and I have also read of posts from others about what causes flares of the pain.
I am wondering if the lower back pain I experience at times could be related to sacroiliitis? I have a significant increase in the pain within the week before my period and it feels like if I move the wrong way my back will go out. I have also experienced an increase in pain to the point where movement is very difficult when I go to Karate class. I stand for 1 to 2 hours often with no times to sit, bowing occurs before all forms, and kicking is part of several of the forms. There is little to no contact, and if any occurs it is light contact with none directed at the area of my back that is painful.
I should also note that I have experienced an increase in sciatic pain when I drive for extended amounts of time. It was particularly bad in my last car where the seat was slightly tilted back so my bottom was lower than my knees.
I have mentioned my back pain at appointments with my PCP and dermatologist. I have not seen a rheumatologist since my derm has been managing meds with overall success in reducing my PsA symptoms as well as clearing up the psoriasis. Both have stated that they do not believe the pain is due to PsA. I am curious about others experience with sacroiliitis and if I should ask them about this. Also, has anything worked in reducing pain? Thanks for reading and any support you may have!