Off sick, return on light duties?

[lelrx]

Morning
I am abit confused about how to go about this but I am currently off due to kidney stones during pregnancy, this is something my gp have continuously missed and its only become apparent during pregnancy and I have suffered alot due to not being able to be treated whilst pregnant
I have had nearly 3 weeks off work, luckily work have put it down as annual leave that I needed to use up so I won't be affected, however this has now ran out and I'm feeling very anxious about returning due to pain in my left hand side and driving to work in stop start traffic as it puts alot of pressure in that area and I don't want it to encourage pain when I actually get to work, my job requires alot of walking around which concerns me but I would be fine if I returned on lighter duties however I have read online that work can refuse this and put you off sick which isn't ideal as I cannot afford to live on SSP
Does anybody know more about this and what my best options would be.
I am also feeling anxious because my colleagues aren't the most friendly and know they have been making comments like 'pregnancy isn't an illness' even though its kidney stones and its actually agonising, I am booking a GP appointment this morning to discuss with them but unsure what my best options are
Thank you