How low test level are you talking about? if you are in the low category of low test level exercise etc might bring your sex drive left. Opioids in general cause low test, did you have low test level before methadone but while on other opioids?
Did you get your test level tested before your started on methadone? Otherwise I cannot really think of and method doctors can use to say that methadone is the definite cause of your low test level. Without a pre methadone test you cannot know if you might suffer from low test due to other endogenous or exogenous sources. How old are you?
There is scientific proof that methadone does influence test levels in men, not how much methadone can influence test though.
And should you choose to take test pharmaceutially you have to take it for several years before your own endogenouss test production will not restart again. But no matter what, having to take one drug, because of another drug one is doing is never a pretty solution.
There is much less scientific studies avaiable about the side affects of bup than there is for methadone due to how new the use of bup is. But as buprenorphine is a partial mu receptor agonist, and not a full agonist like methadone one could hypothesize that there could be less side effects of bup. And the few studies there is tend to show to though more and better studies are needed, but
"A clinical trial (2) compared methadone to buprenorphine regarding their effect on Erectile Dysfunction (ED) and hormone levels. They found that men on Methadone Maintenance Treatment (MMT), but not Buprenorphine Maintenance Treatment (BMT), had high prevalence of ED, related to hypogonadism and depression. However, this study is limited by the small sample size. Another study (3) showed that patients treated with buprenorphine had a significantly higher testosterone level (P < 0.0001) and a significantly lower frequency of sexual dysfunction (P < 0.0001) compared with patients treated with methadone. Again this study was limited by the small sample size" (Fareed, 2012).
The quoted study is named Hypogonadism and Low Testosterone Levels as a Side Effect of Methadone and Buprenorphine, author as stated.