Thanks for query,
Some times due to big ovarian cysts there my be pressure symptoms causing backache
.but sciatic pain is not common.
So pain is due to sciatica
Go for investigations for cause of sciatica. if due to compression of vertebrae there is more damage to sciatic nerve
giving you severe pain
Go for CT Scan and find out the cause and go for treatment.
Consult orthopedics and seek his advice.
ok and bye.