facing something odd with my blog..Please help me..

I am facing something odd with my blog. I am getting many unwanted comments constantly. Mainly from same username with “different email ids”. They are sending Constantly off-topic comments. Not only one user but some users. I am getting 50-60 comments from each username. The main factor is, The comments structure for each username is same. It is working like a machine not human. So please please please help me.. I am Quite afraid of it.Now i am not approving those comments.So please Suggest me what should i do. My blog address is https://www.infotilla.com