It sounds like you are depressed. I would encourage you to seek a counselor or a Psychiatrist if you feel you need medicine to help you. Medicine can really help, when you really need it. Your husband might have a EAP-Employee Assistance Program- where they can recommend counselors and you get counseling for free for like 5 or 10 sessions and then you pay after that.
A Mom's group is a great idea, try meetup.com I belong to one in Mansfield, called Mansfield Christian Mom's playgroup and I love it. The activities have been fun for the kids and the adults.
I'm also in United Methodist Women and we are a group of women across the nation and international that meet for fellowship, and help our missions around the world-to help women, children and youth. You do not have to be a member of United Methodist Church to be in our circle. We meet once a week and there is childcare. If you'd like more info, email me and I'll tell you what we are doing for the rest of the month of December and where we meet. We'd love to have you come and join us!
Do you have a sitter that you could leave your child with occasionally? If you don't, that would be something you need to work on finding someone you feel comfortable with.
Since you've been active in the past with biking and swimming/water polo, I would try to find a group that plays water polo or does bike riding. You could look on meetup.com for groups and this would give you some "me" time and a break from being a Mommy.
I hope this helps, if you need to talk more, I'll be glad to listen. Feel free to email me. I'll keep you in my prayers.