Can folic acid supplements be started after completing chemotherapy?

Hello doctor,

I have just finished six rounds of chemotherapy for breast cancer treatment. Before starting, I was diagnosed with folate deficiency and prescribed six months of Folic Acid tablets. However, my oncologist was not happy with me taking it during chemotherapy so I had to stop after one month. I have now finished chemotherapy and I still have a very sore red tongue and no texture to my tongue or roof of the mouth. I cannot use any toothpaste or eat anything with any strong flavor without an extremely sore tongue. I also have fatigue, shortness of breath, resting heart rate of 90 to 100 and also have angular cheilitis.

I asked my general physician to re-test my hematinics. Now I have finished chemotherapy three weeks ago as I am keen to start taking supplements to help my body recover and because I am symptomatic of a deficiency of folate and/or B12?

Bizarrely, my results say my folate is now 6, hemoglobin is pretty good at 11 but my B12 is 2000. How can this be? It was 500 when they tested me some months ago and told me I had low folate level. I was symptomatic with sore red tongue and loss of texture with tongue sensation. My GP does not understand and is going to ask my oncologist. I am not sure it is his area and I do not want to be fobbed off without it being properly investigated. Do you have any idea what might cause this?

I have started FEC chemo four months back and had four rounds of Docetaxel. I was on Fragmin, Rivaroxaban until for PE prevention of recurrence but had to go on to Fragmin during chemotherapy.