Becca,
Wish I could give you a big hug and make everything better but I will comment.
Strep throat - we are very prone to infections for the first year or so. Short of locking yourself in the house, or not breathing when you are out, you will have infections to deal with. Just try to be happy that there are meds to solve this.
Weight gain is common, especially if you are "down" about how you feel. This is probably the cause of the knee issue. Start walking, try to eat properly and you may end up solving this issue.
Blood flow can also be a post-op issue. Could go away with exercise and weight loss.
Massage will help the back problems. If you can find a chiropractor that does massage therapy, you might be able to get your insurance to cover it.
Try to make yourself smile (physically lift the mouth edges) at least once every hour. You will find this does help make you feel better and more energetic.
Keep realizing this will pass but you do need to be proactive about it.
Good luck.