Hello and welcome to HCM
from your history, they do seem like an
allergic reaction. Clexane as well as
warfarin, does have a possibility of causing irritation and rashes at the injection sites. It can also be an effect of the drug itself, increasing the bleeding and chances of swelling. The reaction can also be due to antiseptic or cleansing agents used at the site before injection, as it did not appear immediately.
It may be an
irritant dermatitis.
In any case, you may clean it with clean water and apply a calamine lotion if there is only itching. If it is very inflammed, you may need to apply a mild steroid like
mometasone cream for a few days to bring it down. take an antihistamine for the itching.
Do consult your surgeon before starting any new medication to confirm whether it is alright. An
allergic rash does tend to go away, but if it is inflammed there is a chance of infection, so it is better to treat it.
If the rashes are spreading, or new ones are appearing, keep a check on what triggers it to happen as well.
hope this helps.