Thanks everybody. You are all so great. Whenever I post about a problem I am having, and get such great replies, I feel like I have just been given a great big hug.
I had a really good talk with my husband about this over dinner. He was so sweet and agreed that I need something of my own. Before our talk, he had been so against me auditioning for a community theater production, because he knows what a time committment it can be. But after I explained to him how I felt, he is now encouraging me to go for it! I feel so wonderful about this. Plus, it will give him some extra time alone with our son on the evenings/weekends, which will not only enhance their relationship, but maybe give him a better understanding of how hard I work all week long!!
Zoebird, you're right, I should invite some of the other SAHM's in my playgroup to have playdates during the week. I'm kind of a shy person so I'll have to muster up some courage to do it, but I'm sure the other moms might be just as much in need of the company as I am.
I forgot to mention, one thing that makes it more tough is that I don't have a car during the week, so I can only travel as far as I can walk, weather permitting.
Anyway, thanks again everyone, you are all great and I am feeling a lot better after having that talk with my husband.