Have not looked at other responses, but you've got a lot going on in your request. I'm not exactly clear what question you are asking, but here is an outsiders point of view:
You seem to be struggling with whether you are being unfaithful to your husband, by having a friendship with your physical therapist.
You are justifying your neglect of your husband sexually (but then say its not hormonal, just not important).
You have pain during intercourse.
You hate the way the stretchmarks make you look.
You don't think you can handle more children but aren't thrilled with birth control and talk about God not giving you more than you can handle.
And why are you noticing other men are attractive? (It kind of sounds like sex is really more important than you are letting on, to me)
It does seem like you have something to be concerned about if you are sharing confidences like these with a man who is not your husband.
You don't want your husband to see you like you are (stretch marks and pregnancy) intimately, but its ok for therapist, because he listens to you. You want advice; here is some that is biblical: FLEE! run out of his confidence and into your husband's.
I remember some of the same exact feelings about sex, pain, stretchmarks, infrequency at about the same year of marriage that you are in. And quite frankly, though you say its not, it is partly hormonal, plus a whole lot of fatigue and insecurity.
Taking some time to just spend with your husband and talk about the sexual areas of your life may open both of your eyes...things got so much better when we did...My husband helped me see that the stretch marks didn't bother him. He was amazed at the incredible act of childbirth and considered them part of this that reminded him of my selflessness. (It was just the right thing for me to hear) Episiotomy scar pain etc. decreased dramatically after the birth of subsequent children and years of faithfulness with eachother covered us with blessings. The stretchmarks fade.
I cannot give you ideas on birth control, nor on feelings of not being able to handle more children, this is something to lay before God, and to discuss with your husband.
I would really stop asking your physical therapist for counsel and look to your husband. If you can't stick to a professional relationship with your PT, get a new one.
ooops...thought it was your physical therapist...its your son...perhaps you are talking too much at his sessions...talk to your husband instead.
Check out: www.aboverubies.org