I am sorry to hear about your issues ...
As you have had stress fracture in sacrum , for pain relief , yes you can ice .
As far as management of Sacral stress fracture is concerned first step is pain management , A variety of analgesics that act centrally, such as paracetamol and opioids, are available in clinical practice and they should be used until pain resolves.
As you have osteopenis ( Low bone cells ) so for that you can ask your dr for Bisphosphonate injection to strengthen bone .
Along with calcium and Vitamin D .
As far as your question of early mobilization is concerned , An important question that arises with sacral stress fractures is whether to permit weight bearing, or to treat patients with bed rest. Conservative management usually forces patients to stay in bed for 3–6 months, which may increase to a year in the case of poor bone healing. The risks of such a long immobilization are high and they may result in accelerated loss of bone mineral density, increased incidence of deep vein thrombosis, pulmonary embolus, or loss of muscle strength . In order to avoid or minimize these adverse effects, a rapid return to an active life style with an early mobilization for stable sacral stress fractures which don’t require surgical intervention should be recommended. The advantage of an early rehabilitation is the stimulant effect of weight-bearing and muscle tension on osteoblastic activity, which results in bone formation, whereas a prolonged bed rest may cause unrestrained osteoclastic mediated bone resorption.
You can start gradually your daily work , but avoid lifting heavy weight , excessive stress and start medication please as I mentioned .
Regards ***** ***** luck .
If you have further quires let me know please .
Don't forget to click on good rating , as I will be paid only when you rate my answer .