I have no adverse effects on my character that I can see, but that "bomb" icon (I think that's burden) flashes once every 10 seconds or so ... no idea why

Are you running any mods? The default icon in most mods for custom spells is the bomb icon.

Bunch of mods ... no spell mods though ... just started and I'm 10 hours into the game ... hmm

When I play as my Argonian I get told "you are overencumbered" quite often when I'm not, even in the menu.

Got any of Duke Patrick's mods? He's got one that lets you know about sicknesses, and another that lets you know about stat/attribute losses, if I recall correctly.

It's a mod's script effect, they use the Burden Icon. I know that that 28 days zombie mod spams them very commonly, not sure about other mods.