Retail work at 36 weeks is genuinely tough on your body, so I understand your frustration, being on your feet all day at that stage is no joke. One thing worth knowing is that in Singapore, maternity leave can actually start as early as 4 weeks before your due date (so around week 36), meaning you could ask your employer to begin your official maternity leave now rather than waiting for the birth. If your doctor won't give HL, it might be worth requesting a referral to a specialist or trying a different doctor at a polyclinic, since some are more willing than others to document physical strain at this stage, my friend went through something similar in retail and got her leave sorted after switching to a different GP who was more understanding about her back pain and swelling. The trade-off with starting maternity leave early is that it eats into your post-birth time, so it's worth weighing whether the rest now is worth having slightly less leave after baby arrives. Either way, do keep pushing, your health and baby's wellbeing come first.