Drop in platelets 3 years post BMT

Hello all-I’m back to this group because once again I’m lost and searching for answers. This Easter Sunday is my husband’s rebirth day, 3 years post bone marrow transplant for MDS. On March 3, his labs showed platelets at 55; a week later they were at 18 and have remained there since, ranging from 22 (once) down to 5. He had a bone marrow biopsy on March 13 and we’re still waiting for some of the results. He’s been in the 50-77 range for the past year, and his oncologist said sometimes it just takes longer for them to come back in some people. Does anyone have any thoughts or experience with this type of situation? Thanks in advance.