I have erysipales in my groin. I'm treated for that and im in bed for a week. But now I saw round my anus is dry and red. What is that?

Yeast infection. Probably a yeast peri recital infection cause by yeast overgrowth due to your antibiotic treatment. It can be cured with oral swish and swallow Mycostatin (nystatin) suspension and topical lotrimin cream to the rectum. If severe or unresponsive oral Fluconazole could be used.
Hard to tell. Erysipelas is a strep infection of the skin and is not that common nowadays, so I am not certain what you have (had) in your groin was true erysipelas. I am not sure what you have around your anus other based on the extent of information you provided. In case you were treated with antibiotics, you may have developed side effects, but I would have genital herpes ruled out first as it may be that.