How much can you trust your body?

I hear woman say that they know exactly what is going on in their bodies. They know exactly where they are in their cycle and how they are supposed to feel in every step.
Is it because they don’t need to listen? Is it because they don’t have to look at every strange little phenomenon and because of that it doesn’t really matter what the body says?
Not listening and not knowing, is that what makes the bodies signal system very clear and easy to understand?
For me is it the opposite! I listen to every little strange sound, every little odd feeling, and every peculiar twitch and it doesn’t make sense.
I haven’t got a clue to what my body is up to! My breast hurts, well that is a pregnancy symptom, or is it just a symptom of all the medication I put myself trough? Even though they usually don’t hurt, does that mean the medications finally are working, and so is it the medication or an early pregnancy symptom?
My lower back hurts! Is that the first signs of AF or is it the uterus stretching to be cozier for a little embryo?
I feel a little nauseous, is that a side effect of the drugs or is it the first pregnancy symptom?
I am in a terrible mood, is that PMS or is it just me going nuts trying to listen to all signs from my body?