Anal fissure & sphinterotomy 5 weeks ago. 90% healed. sometimes just pass gas unexpectedly. ugh! will that go away or how long will that be like that?

Yes takes time: After your type of surgery, possible to have some loss of voluntary control and flatus incontinence , with healing and time you will over come it , start doing sphincter exercises ( contracting and relaxing the anal area) speak to your surgeon.

Usually temporary: Temporary loss of control to gas and liquid stool is occasionally seen in patients after undergoing sphincterotomy for anal fissure. Sometimes this symptom can last up to six months. It is rarely permanent. You can do kegle exercises that may help.