Why do I feel like there are spiders crawling on me when there isnt?

Hi. Okay so I'm seriously starting to get frustrated with this little problem I've been having that started about a month or so ago....I'll just be sitting or standing and it feels like there is something crawling on me on parts of my body but when I look down there's nothing there. It literally feels like a bug is crawling on me and sometimes it stings like I just got bit...Does anybody know if maybe I have some type of skin condition or if I'm just crazy???? It's really starting to freak me out so the sooner someone could help me out the better! Thank you