I must have been really lucky with my yeasts so far but usually my beers turned out nicely carbonated without any priming. The last batch though is really flat. Is it still possible to prime in the bottle, i.e. open the bottle insert the desired amount of sugar and leave it to carbonate?
On my first batch I had the following issue: knowing very little about brewing and even more about what "fermentable sugars" are, I primed used raw cane sugar I had first burned into caramel, for some extra taste. The result, of course, was a beer with almost no alcohol. I discussed this with more experienced home brewers and what they advised me was the following: dilute the wanted amount of sugar in as little water as possible,boil it for sanitation, sanitise new caps, open all your bottles and pour the corresponding amount of sugarwater in each using a simple syringe,then recap. It worked just fine, my beer carbonated normally and I didn't have any contamination issues at all. Go for it!