Hello, I'm Dr. Deb.
I recently came online and see that your question about Gus hasn't been answered. I'm so sorry that you've had to wait for a response, but if you still need assistance, I'd like to help if I can.
Constipation issues are actually more common in cats than you might think although I don't become terribly concerned unless a cat hasn't had a bowel movement in about three days.
But, if Gus were my cat, I wouldn't want to wait another day to see if he'll produce stool on his own. There are several over the counter options for you to consider in addition (or instead of) the hairball laxative you've been using.
1. I actually recommend about 1 inch of hairball laxatives 2-3 times a day so you might increase the amount you've been giving.
2. Canned pumpkin (NOT the pie mix) at a dose of 1/4-1/2 tsp per day. You might be surprised how well cats like the taste of it.
3. Over the counter, human Miralax at a dose of 1/8th-1/4th tsp daily which can be increased until soft stools are produced.
4.Raw bran flakes (wheat bran, not cereal) in canned food
1/4-1/2 tsp daily although this isn't something that many cats like.
If you aren't currently feeding Gus canned food, this may be something to consider to prevent future episodes. There are prescription diets also available for those cats with chronic problems, but this isn't something that I'd recommend for a cat this age at this point.
I hope this help although, again, my apologies for the delayed reply. Deb