My 3 1/2 month old won't sleep with or without swaddling! HELP!?

My baby girl uses to LOVE being swaddled. It was the only thing that comforted and soothed her AND put her to sleep right away. Here recently she started mildly resisting being swaddled... so I would let her nap in her swing without it occasionally and she did fine. She has always been a great sleeper and even usually falls asleep right away. Tonight, however, she squirmed and screamed when i tried to swaddle her. NO dirty diaper, just fed and burped, DEFINITELY tired. I figured she just didn't want it anymore so I let her lay in her crib to fall asleep. She wouldn't. I stayed next to her crib (hidden) for 1 hour, occasionally trying to comfort her and put her pacifier back in her mouth (usually she only keeps her paci in for a minute or 2 before falling asleep and spitting it out). Finally, she was so tired and worn out, (so was I) that I gave up and swaddled her. She was asleep in a second. She won't sleep with one arm out... (have tried that in the past) Any suggestions?