Beer not carbing

I think this gets posted about once a week, but i've finally had a beer not carbonate and I'm wondering what I can do?

So here's the story: 4-5 weeks ago I had a particularly ambitious day. I brewed a batch, bottled my IIPA and my bitter. For the IPA I did the standard 4oz of corn sugar. For the bitter(I don't have my notes in front of me with the exact measurements) I used some wheat DME and some table sugar.

Sanitized everything as usual. At that time the ambient temp was about 80 degrees, and 68 in the cooler parts of my house(where I was fermenting). So I figured, what the hell lets get this carbed up quickly, and stuck the beers in the garage where it easily gets 15 degrees hotter than the ambient temp.

Anyway, two weeks go by and we have some cooler nights and it gets to about 55 at night so I decide to move the carbing beers into the fermentation room, after they went through about 3 nights of this. At this time I tried a 12oz from each batch. The IIPA was almost totally carbed, and the bitter had a very very faint hiss. But no carbonation. 3 weeks since then and I'm half way through the IPA and the bitter has not changed at all. I should also add there's hardly any yeast in the bottles of bitter.

So what are my options? Currently I'm sitting them in a room by the heater keeping it a constant 70F. I need a contingency plan though, suggestions?

If you got a faint hiss, your beer is carbonating. The amounts of DME/sugar used are relevant, so you'll want to figure out what those are to troubleshoot. If you carbed to style (i.e., very low), you probably just haven't given the things enough time yet. There's plenty of yeast in there.

For 2 weeks the beer was at a temperature colder than it should have been so you lost 2 weeks of time. DME takes longer as a primer because it is a complex sugar the yeast needs to break down and 3 weeks at 70 is the minimum amount of time recommended for priming.

Bigger beers will take longer as well. If there is a hiss it's carbonating and just needs more time so be patient and they'll get there

I'll find the measurements of priming sugar when I get home.

For the sake of clarity, the beer was not left at 55F for two weeks. Rather, it was brought to 55F for two nights while in the garage. The garage was atleast 70F during the day.

I've always heard DME takes longer; I've used it before three times and it hasn't taken anywhere near this long.

Time heals all wounds, so right now im letting it sit at 70F, and I'll try again in a few weeks.