I am so sorry to hear your rabbit is in distress. Although I am not a vet, I can point out ome possibilities and give you an idea of critical symptoms. (See below.) After reading, please be sure to rate my response so that I can receive credit for it. Thank you.
There are numerous causes that could lead to hair loss in your rabbit. The mites may not have been eradicated completely.In order to avoid re-infection, it is very important to thoroughly clean the cage and exercise areas after treatment for mites, because fur and dander that have been shed may leave mite eggs in bedding or other locations.
There might be an underlying or secondary infection, or the hair loss could be due to a hormonal imbalance. If a rabbit's skin is chronically exposed to moisture from a leaky water bottle or damp litter, for example, then hair loss may follow as well. Of course, it could be possibly due to overgrooming or heavy molting.
There is no way of telling definitively what's going on until your rabbit is seen by the vet. At the upcoming appointment, s/he will be able to make a diagnosis and tell you what steps to take. However if any of the following symptoms is in evidence, then please take your rabbit in immediately for emergency care: blood in the urine; heavy, open-mouthed breathing; enlarged abdomen; limp, floppy, or hunched up posture; vocalizations that seem to be due to pain; extremes of temperature; or the rabbit is not eating or not excreting.
Please let me know how things come out for you. Also, feel free to ask any follow up questions at no extra charge. Best regards, ***** *****