Worried about skin cancer...?

I know this is probably a bit hypochondriac sounding, but I was watching a youtube video about melanoma and I got really scared. I have light skin, hair and eyes, and tons of freckles and moles. The problem being, there are so many, and I wouldn't be able to tell if I got a new one. Lots of them are weird shapes, and some more than one colour. I have had quite a few bad burns in my life, and my grandma died of melanoma. There is also a weird spot under my arm that started off big and red and slowly got smaller and darker. Now its black. Should I be worried? My dad also died of cancer, not skin cancer, but I have always been worried. Any help would be appreciated! Thanks!