Botox results wears off after 5 weeks. I'm a 40 year old male.

Hi Pedro, I’m sorry to hear that you’re struggling with this problem. Botox generally lasts 3-4 months. I wonder if you find that your treatment wears off in some areas sooner than others. In certain injection areas, such as around the eyes or above the lip, a very small amount of units are used. Because the duration is dependent on the number of units used, patients find that results in these areas wear off faster than other areas, like between the brows where a larger number of units are administered.
If this is the case, it’s possible to go in more frequently (every 6-8 weeks) to treat these smaller areas. You would continue treating larger areas every 3-4 months. I recommend seeking out a board-certified aesthetic dermatologist who specializes in Botox injections. An expert in injectable treatment will be able to work with you to develop a treatment plan to best overcome this issue. 

Quite a frustrating issue.  If you get Botox more often than every 3 months, you may develop antibodies to the structural proteins it is manufactured with.  This may be occurring already and might be one of the reasons it's wearing off.  Another reason why it may wear off quickly is that you are not receiving enough units, just as you thought, but you have already tested that possibility.  Lastly, please make sure you are getting injected by a reputable office.  It is quite easy to "water down" Botox or to use "black market" Botox and the consumer (you) would never know.  I would recommend trying Xeomin which is another botulinum toxin that is not manufactured with any structural proteins.  Therefore, there is no possibility for you to form antibodies to it.  It works the same as Botox and lasts just as long.  My patients absolutely love it.  I hope this helps.  Good luck.

Men tend to have stronger and bigger muscles so I typically need to inject more botox to treat the top third of the face - 60 to 80 units - than in women.  Consult with a board-certified and experienced cosmetic physician.