An infusion is IV iron. It drips slowly over a period of hours. It typically takes 1-2 weeks for your body to absorb it fully and put it to work. A transfusion is blood. I have had both, although the transfusion was given during surgery so I don't know how long it took, if there was discomfort, etc. as I was heavily sedated for days afterward!
You can be bleeding and not see it in your stool and/or you may just not be able to absorb it properly in your GI tract, which was typically my problem. The IV iron can make a huge difference. IF you are really low, it may take more than 1 infusion to boost you back up. Your hematologist will want to monitor you carefully by looking at your iron stores periodically (ferretin levels in your blood). When I dip low, he usually calls me in for an infusion. Infusions can allow you to rebuild your iron stores up vs. receiving donated blood via a blood transfusion (but will boost you more quickly).
The first time I found out I was anemic (at a 7.0) I didn't realize it! My doctor noticed my pale gums and suspected. I was out of breath and exhausted all the time--just figured I was out of shape/getting old! Now, I know my signals and try to stay on top of it. I have never been able to tolerate oral iron pills so it is infusions for me!
I hope you feel better soon!
Ohhh thanks for clarifying! Yeah I had the iron infusion while in the hospital so I guess the hematologist will be monitoring me when I see him. I have to make an appointment for this week for some shot I think he was saying and I'm guessing more bloodwork. Blehh I hate needles and blood with a passion..I was always terrified. It's actually a bit sad how I'm getting used to it now since I have bloodwork done so often (doesn't mean I hate it any less though, lol!)