Well Mikey, at the very least this may be a good, (and most likely necessary), time to change your mail password.
Make it a nice long, incomprehensible, one while you're at it.
The newest iterations of Firefox have a password manager built in. I'm not vouching for it mind you. However, I do use it, and it seems to work OK.
Every once in awhile, I get phone calls telling me, "there's a question about your Amazon account", followed by a high dollar charge that, (allegedly), needs to be dealt with. I sometimes pick up the phone and screw with them, sic. "wait I have my computer running, so let me go over and check on it". A click, a long pause, and then a dial tone usually follows.
Now, in your case, if these messages are coming too close in time proximity to something you have actually ordered, or are expecting delivered, it might not just be "coincidence". There does exist the possibility that you might have picked up some kind of malware during one of your "adventures".
I'd suggest a thorough scan of your system drive (C:/), if only to calm your obviously frayed nerves.