Aw, mama, that's really tough, third trimester pa lang at nag-start na, laki ng stress with diabetes pa naman. Sitz baths are actually legit and maraming kaibigan ko did that, usually 10-15 minutes a few times a day sa mainit pero not too hot na water, and honestly nakatulong sila to ease the pain and swelling, though results vary per person. Since ilang araw na lang before your due date at may diabetes ka, I'd really suggest follow up with your OB again or ask specifically if may safe topical options pa for third trimester, or if kailangan ng referral sa ano man specialty, sometimes kasi may alternative remedies na safe in pregnancy na hindi pa mentioned. Drink lots of water din and try to avoid constipation kasi yan talaga yung trigger, and after birth usually bumabalik to normal na. Sending you strength, mama, almost there na!