A question about a vibrator that I have

Yes, it's time to throw it out. Jelly breaks down over time and some people are sensitive to jelly products. And I wouldn't call it an allergy...just a sensitivity...

In the long run, you'd probably do better to use silicone, which is more expensive initially but won't need to be replaced for a long long time. But if you have your heart set on jelly, then you should DEF use a condom over any jelly toy in the future.

You have to throw jelly toys out whenever they get sticky or start to smell bad.

Yes, the jelly break-down process is most likely responsible for this irritation. Jelly has phthalates- chemicals which make it softer but are also very bad for your body.
Use a condom over jelly toys to protect yourself, and extend their lives, or go for silicone.

You know, they often smell bad right out of the package, but you're probably talking about a different kind of smell.

I was gonna say, don't jelly toys always smell bad?

I agree with everyone else; condom it up, or get a phthalate-free toy. However, it's also possible you've got some sort of infection; it could be bacterial, viral, possibly an STI, or bacteria vaginosis (assuming you have a vagina). If changing a toy doesn't help, I really suggest heading to a doc to get it checked out. Infections in your nether regions are NEVER fun!