Hi there, good on you for entering recovery!
I did the first part of my recovery in hospital as in inpatient and the first two weeks i gained a fair bit, some of which was fluid retention, as your therapist says. Then the third and fourth weeks I hardly gained anything on the scales but visibly you could tell I was regaining some body weight, not just fluid. Then from the 5th week onwards I gained about 1.5kg a week and I was released at BMI 18, then proceeded to gain a few more kg at home so I am BMI 19.5 now. Keep going, the yucky water weight will subside and you will start to feel so much better and more alive again. PS the type of food you eat has alot to do with fluid retention.
The side effects of allergy medications keep some people from using them. Natural remedies can be a great alternative, but some are more effective than others.