if you have low ferritin/iron deficiency, is it safe to treat with B12 at the same time or should I wait till after?

I did read the guide about taking an aggressive approach when treating this, but I have gastritis and want to be careful.

im hoping to hear personal stories of people who have dealt with this sticky situation.

my symptoms: unrelenting nausea, so much hair shedding, lack of appetite/weight loss, bone aches, high heart rate, scalloped tongue, muscle twitching, heat intolerance, shortness of breath