I did gain on Elavil but I was on 50mg a day. I probably gained a total of 30 lbs but it helped the pain.
After about a year it stopped helping and I was weaned off. In the last 2 months without dieting I have lost the 20 of 30 lbs that I gained.
I believe the Elavil caused me hunger so I did notice the calorie intake was higher.
You are on such a low dose that IMO I wouldn't worry about it right now. If it is helping, to me it is worth it.