I made lots of cuts on my forearm with scissors and after 3 days my skin became really hard and my whole forearm is swollen. I put polysporin on everyday. Is this an infection?

It might be. Objects such as scissors are not very sharp and often not particularly clean, which can make an infection more likely. I would recommend going to see a doctor that you trust to have a look at it. I personally experienced that doctors are very professional and calm when it comes to the treatment of self harm wounds. If the idea scares you, take a friend with you. I can understand that this might not be an easy step to take but it’s important to make sure that these wounds are taken care off probably. I wish you all the best!