Might have a swollen gum?!

Ok so this morning i woke up and behind one of my teeth, which for about 2 years, 4 years ago, had intense dental work. That's one reason why I'm concerned - the other is that I'm due to go on a GCSE Spanish Trip tomorrow. I looked at the checklists for bleeding gums: I have changed my diet recently and last night i made a detour (because it was saturday), i have had a rather bad cold the last couple days, I came off medication i'd been taking regularly for a year a month ago, just gotten a new toothbrush, and yes whenever i brush since i was young i always spit out blood at the end.
The sore is purple-red (like a closed sea anemone) and is a tad sore when you touch it.
help would be greatly appreciated.