How long has this been going on?
Do you have any health problems?
Any other symptoms?
I am wondering if you are having some nerve involvement due to your back surgeries.
If your socks are leaving marks, and this is new, you may be having some swelling that you just can't tell is there because it is slight, or has been so gradual, it looks the same to you. Some swelling can make your feet feel "tight"
But, the numbness may be due to some residual or new effect of the back surgery. Numbness often times involves some nerve compression.
Please speak with your physician. You may benefit from a small diuretic to use occasionally, but an examination certainly would be in order. I wish I could tell you exactly what is going on, but I think you can get some relief, if not resolution of your symptoms.
I hope this was of help to you. Please let me know if you have any further questions or concerns.