Maybe we can analyse the horoscope behind your question. You have a big, kind, caring sun conjunct Venus in motherly Cancer, trining a psychically sensitive moon-Neptune. I wonder if you are at least somewhat psychic! But your sun-Venus is opposed by Saturn. Saturn is the planet who can make us feel inadequate or not good enough. So you may be hard wired to want to take care of people, whether they deserve it or not; and whether they are at all grateful or not.
I note that Saturn is in your 5th house of children. I don't suppose you have something like an older "boomerang" child at home who is causing you concern?
Being "Assertive" about your "Feelings" seems exactly to define your moon-Mars opposition. Neptune in the mix tends to dissolve what it touches, so perhaps you have some ambivalence as to what your feelings really are, or how to express them.
I dunno, Melisa. To me, the way to express your feelings is just to express your feelings. And then just acknowledge that it doesn't mean that the people who receive your communications will behave differently because you do so. They might feel hurt, angry, or annoyed as much as they are likely to feel whatever you hope they will feel. You probably know this, and timidity about a potentially negative reaction is what holds you back. If you have something to say, say it; and then just prepare yourself to stay calm and determined through whatever happens next.
If you wish to work on your Mars nature, I always feel that some type of athletic activity or sport is a good way to strengthen your Mars muscles. I wonder if such a water-person would be happy working out in your local rec center swimming pool. Even if you don't swim a stroke, they will probably have an aquatic exercise class designed for non-swimmers. If you do not have a regular fitness program now, see whether developing one strengthens your self-confidence.