1) If you want to take the allergy route, try Bendryl first so you don't spend too much money on grapefruit seed extract. I tried it the other day just for the hell of it and my lips were really 100% normal. One dose of 2 tablets should suffice to see a difference (if you do have an allergy).
2) If using glycerin, make sure not to get any on the outside of your lips as it'll cause clogged pores. I learned the hard way. They're barely noticeable but, of course, I'd rather not have them. If you get them, just sure to exfoliate with a wet face towel once a day or so.