So sorry for anyone else having to go through EN. One of the difficulties is you are in pain and sickness and you dont look sick. The fever is low grade. Tell others you have an auto-immune disease since most people these days know what that is. Don't waste your breath and energy explaining it because seriously most people dont get it. If you tell them its a type of skin disease, some people think they can catch it. Take care of yourself! Make sure you rest with legs elevated. The beginning of the disease is the worst with weakening, diarrhea, low grade fever, nausea, before the onset of the lesions. No, you don't have a fever over 99.5 but believe your body is sending all of its energy to attack itself and make you better, auto-immune disease. The major way you get over this disease is by resting. Let your family know you need their help. Having it for the first month is purely exhausting and I am athletic.

**You have to keep taking the ibuprofen even when you think it is gone and you're feeling great because it will come back worse with a vengeance if you don't. This happened to me several times when I stopped ibuprofen too early. You can back off the doseage to 400-600 mg 3 times a day but dont take it completely away until you are sure its gone.
I had chronic erythema nodosum which was not recognized yet by most doctors as "chronic" for a long time from 1986 in college to 2002. Mayo was first ones I knew of to do this. I still have written it down on my chart and had doctors tell me there is no such thing, ha! While I could reproduce the articles for them I just nod my head and know that most people are ignorant on this subject. Why? Truly I was told by doctors not much research has been done. People don't die from it if they have been extensively poked, prodded, chest xrayed, blood tested, eye checked, etc., and found nothing else wrong. With my first diagnosis in 1986, my father was a ENT at Barnes St Louis so he took me to his doctor friends, my shoes wouldnt go on because swelling came on so suddenly and I had no meds, anti-inflammatories. A bunch of specialists came into the room, med students, camera man, to take pictures for books. Then they put me on high doses of ibuprofen, 800 mg three times a day. It took about 12 weeks before I started feeling like I could walk without pain. I continued to have this once a year to year and a half for 10 years. I still had 2 lesions on my legs for awhile after recovering that remained there for a few years. I told my dad who again was a doctor, I really thought those two lesions were not just residual bruising and/or permanent joint damage but erythema nodosum still active. He believed me and asked me if I wanted to have a biopsy there. It was in a bad location for a biopsy (still have a scar) but I was game. After the biopsy the lab showed positive results for EN! I felt justified because everyone acts like you should be fine, it's gone. But, I can tell you from this and having this sooo many times, that one or two can remain for awhile. Mine went away about 2 years after that initial. I still have tenderness and discoloration, darkness in that area and in 2 others that is permanent damage. (I have very white skin.) I can run without pain. The biggest way I notice it is if I am sitting on the floor. I can't cross my legs normally.
As far as medicine, best thing is taking non-steroidal anti-inflammatories NSAID consistently 800 mg ibuprofen or naproxen if you can handle that. Dr put me on Naprosyn i.e. Naproxen before it came onto the over the counter market. 800 mg 3 times day. It hurt my stomach badly so I asked to go back to ibuprofen.
As to why you have it, I was tested over and over again first 5 times by specialists for Sarcoidosis, strep throat, lupus, rheumatoid arthritis, etc. Doctors told me after that, unless it was bad, I didnt need to come back. I did get EN again 6 years later ( month after getting chigger bites all over my legs) for the last time in 2001, it was the worst case I had. Lesions all over shins, both upper legs and thighs, and two on forearms. So painful! I couldnt work for 2 weeks. New doctor, dermatoligist, thought maybe I had something like lupus while I told her EN with unknown cause. Ran tests and had a biopsy and findings again were EN. Had me again take ibuprofen nothing else.
I have never posted to a medical site. Hope this helped. Take care! Sending prayers your way!