Hi, and thank you for coming to JustAnswer.com with your question.
Being that you had a suspected allergic reaction you should absolutely NOT take it again until you find out for sure if you are allergic or not.
Even though it looks like chances are that you are not - the risk is not worth taking the chance.
If the clogged milk duct has caused mastitis then you can speak to your ob/gyn to find out what medication you should use instead right now.
Also, I am assuming that the midwife told you that the best treatment is nursing (expressing milk) and warm compresses?