Pulmonary embolism? Could I die?

Out of pure curiosity so I know for the future, what differential would it affect?

I suspect OP has already gone to the walk-in centre, but would 111 not refer to the ambulance service being a chest pain call, despite the low likelihood of anything major?

1. A heart attack in an 18 year old would be exceedingly rare.
2. Even from the vague symptoms OP has described, it does not sound like a heart attack.
3. Even if it was, it's unlikely that aspirin would have any benefit after 3 weeks of symptoms.
4. Alternative diagnoses like gastritis are far more probable and aspirin would only serve to exacerbate the problem.
5. We know nothing about OP, who may well have asthma which happens to worsen with aspirin.

All in all, advising someone to take aspirin should come from a medical professional who has assessed OP properly.

1/2. Yep, no doubt. Though it also has proven benefit for angina (again, of course unlikely) and PE (likelier, but still unlikely, though we don't have a full history). http://circ.ahajournals.org/content/125/10/e439.full.pdf Unfortunately, this: http://smchealth.org/sites/default/files/docs/388374270Aspirin_in_ChestPain_Update.pdf is the best source I can find re aspirin in flu-like chest pain, but I can't find anything that suggests against it either.

3. Probably not, but I'd say the risk of 75mg of aspirin (what most people will have) is pretty low, and it at least has a chance of helping.
4. Gastritis? What makes you think that? That's not normally associated with chest pain, surely? Would flu (or similar) not fit better?
5. I would hope people read the contraindications before taking medication (and I would imagine they would've been told they can't have aspirin when they got the asthma diagnosis).

1/2. Yep, no doubt. Though it also has proven benefit for angina (again, of course unlikely) and PE (likelier, but still unlikely, though we don't have a full history). http://circ.ahajournals.org/content/125/10/e439.full.pdf Unfortunately, this: http://smchealth.org/sites/default/files/docs/388374270Aspirin_in_ChestPain_Update.pdf is the best source I can find re aspirin in flu-like chest pain, but I can't find anything that suggests against it either.

3. Probably not, but I'd say the risk of 75mg of aspirin (what most people will have) is pretty low, and it at least has a chance of helping.
4. Gastritis? What makes you think that? That's not normally associated with chest pain, surely? Would flu (or similar) not fit better?
5. I would hope people read the contraindications before taking medication (and I would imagine they would've been told they can't have aspirin when they got the asthma diagnosis).

What qualifications are you basing your teatment of the OP on? You've just gone and instructed someone you've never met before whose medical and drug history you know nothing about to start a specific pharmacological intervention as treatment for some symptoms you've no confirmation of. While well intentioned, this isn't safe or sensible, we ask that people give general advice on here rather than specific medical advice.

I wrote a post responding to etomidate, but I've deleted it. My SJA trainer instructed to play it safe and give aspirin for chest pain, but you're right, I shouldn't have said to do so without a history. I apologise, and withdraw my statement.

Thats OK, I get that you meant well by it. Wrt what your SJA trainer told you, I'd leave giving drugs like that to medically trained staff, in the end they have the training, accountability and most importantly are insured to do things like that, I don't know if as a first aider you'd be covered (I doubt you would) if a patient were to suffer ill effect from a medication you gave them.

But what if the internet is right?