Intense itching & rashes. Sort of sti?

From last 20 days i am having intense itching on my whole body then when i itch rashes start to come . I have never had this problem this has happened only after i had sex with my bf for the first time . i mean we had sex before 50 days and the rashes came 28 days after we had sex . I also had a yeast infection and few pimples on my vagina as well . The rash is very itchy and comes and goes .last time i had it for 3 to 4 days maximum .I had a medical abortion as well that is 43 days before from now .Is it some sort of STI??? Coz all this has happened to me after i had sex with my bf . I forgot to mention the rashes occur on my back but very much on my arms above elbow . i had few rashes on my breasts as well for 2 days . I used to take cetirizine and they used to go .they are recurring please help please please .