Steroid injection in the beard for hair growth can cause side effects, like stretch marks or any other ones?

Genetic androgenic alopecia can start with puberty so you may be seeing early signs.  You need to see a doctor for an exam if you want a diagnosis.  There is no way to completely stop genetic hair loss.

It is difficult at times for patients when they do not see results.  Sometimes this may mean that the drug is not working for you.  It does not work on everybody.  Taking a higher dose may not be the answer.  In fact you may have side effects.  

You generally cannot "stop" genetic hair loss.  There are medical and surgical treatment options but these are not "cures".  You first need to see a doctor for an exam and establish a treatment plan.

Minoxidil 5% is what is recommended for treating hair loss.  Higher strength does not always mean better results.  Higher strength can actually have greater risk of side effects.  No studies show azelaic acid works for hair loss.

Genetic androgenic alopecia is a trait you are born with.  Taking medications will not stop the hair loss.  Propecia is a drug men take to slow down the hair loss process.  It does not stop hair loss.  Avodart works in similar ways as Propecia but is not FDA approved for...

If you just consider kenalog by itself, it can be a cause of hair loss.  In general, it may take over a year before you see hair regrowth.  However, there may be other reasons for hair loss that you are not aware of.