I agree, calamine lotion works wonders for all types of itching caused by bug bites. That is a really big scab, though...
If it breaks open, I'd suggest putting some antibiotic ointment on it, just to make sure that it's not infected (which might be the cause of the itching all over your knee).
I think the itching should go away soon, though...usually such bites have effects that last about a week with me.
Just apply calamine and that should well do.
whoops i thought i had a mosquito bite on my knee is what i meant! :)