Retarded glitch

I didn't have this problem until I started playing campaign again this week (had only been playing multiplayer when bored), but my primary weapon doesn't show up anymore. The guy's hands are still in the position as if he's holding the gun, and my ammo is always full (obviously because I can't use any of it...), but the gun doesn't show up. I can't shoot or melee with it. When I pick up a new weapon to replace it, like the Smartgun, that shows up but then disappears as soon as I get to the next mission and I'm *beep* again.

What the hell kind of glitch is this and is there any way to fix it? It's pretty retarded that I have to rely on my secondary (shotgun) and my pistol to get through levels. Granted, the game is easy and I can do it, but it'd be a lot nicer if I actually had my goddamn pulse rifle.

Cena doesn't overcome any odds. He's a wrestler with a God mode cheat on.