Eczema or something else?

Hi all I know this is a baby group but I don’t really have another group where I could ask..

I have this patch of skin on my knee which is painful when I kneel down to change my son or something, it has grown in size and I’m worried about it but I don’t want to waste the doctors time if it is just a patch of eczema/dermatitis or something.. has anyone had or seen something similar? Thank you