Can I use hydroquinone and Retin A after a beard transplant?

Hi, it is not uncommon to have some discolouration post-transplant over the recipient area, be it scalp or facial area. 
1.5 months post-transplant is still considered a fairly short period. 
It could be due to residual bruises or post-inflammatory hyperpigmentation.  Most of the time the discolouration is just a transient one and with time, the skin colour will slowly return to its normal colour even without any intervention.
Nevertheless, it would be best that you could visit any certified hair transplant doctor in your community to get it examined. Hope it helps, cheers.