I really agree that a few years of nursing under your belt will make you a much more useful volunteer. In situations like you describe you are not going to be considered an extra pair of hands, rather they will want you to be an expert. Being willing to learn is nice, but it doesn't go very far. There are many small organizations, and they might be willing to take you, but they will not be training you, if they had time to train, they would do the appropriate thing which is to train the local people who plan to live there forever. You always have to think about why they need you in that organization. Organizations like IRC use Nurses not as nurses, but as managers and teachers, so you need to have some experience, so you can effectively manage and teach, otherwise it is a disaster in the making. This, I realize is not widely known, because all the photos show expats giving care, which might be about 10-15% of your daily duties, but it looks more interesting than showing expats tearing their hair out over a duty roster.
All that said, there are many many good organizations which can offer you two to 4 week opportunities where you can experience the culture, learn, work with physicians close by, etc. Although some of these are somewhat not so great projects ie they do not benefit the community long term, You can get a feel for things, and it looks good if you do decide to work with ICRC in the future.
Also agree with another poster, working with the really disadvantaged here in the US can put you in a good position in the future.