3 months post Hair Transplant. I got mesotherapy injections into scalp, will this affect the blood circulation?

The therapy you had should not have a negative impact on your hair growth (hopefully the opposite!) It is still early in the process and this is about the time when you will start to notice some growth.Be patient.

Hi there, in the early phase of a hair transplant, we are expecting a shedding phase first, follows by a growing phase. At this 3.5 months point of time, we are looking at a growing phase.
Nevertheless, the growing speed varies according to individual and it might not be apparent to self yet. 
Scalp Mesotherapy is a general term for multiple injections of minute volume of specific substances onto the scalp. The substance could range from vitamin, mineral, medicine, peptide, exosome, prp, autologous skin micrografting to even stem cell.
A lot of hair doctors would agree to perform some form of mesotherapy to the scalp, post-transplant to provide more mediators and supports for the hair growth.
Hence, give yourself and your transplanted hairs some more time. Nevertheless, if you are still in doubt, it would be best that you could visit any certified hair transplant doctor in your community to get a thorough check. Hope it helps, cheers.

Dont worry!
You are doing the right thing! Most hair transplant surgeons recommend mesotherapy PRP post transplant to ensure viability of the transplanted hairs especially if you are using your one platelets there will be no rejection!