Hello respected, 
i think you are having a scar mark at the site of 
spider bite, that went to dryness and all problem started , many 
scars has tendency to dry and convert to 
eczema, if it is itching than there is more chance of eczema.
so in my opinion you should apply good quality moisturizer creams, not lotion along with 
clobetasol cream to suppress inflammation, avoid ulcerative areas.
use proper antibiotic creams at ulcer sites.and consult GP if 
oral antibiotics needed for ulcer,
take oral antihistamines like levocetrizine 10mg at night time for itching..
Once it's better , continue moisturizer creams ..apply moisturizer 3 to 4 times a day,
Thank you , get well soon