Breathing Problems/Chest Pain feels like a bubble...

Hi
I will start off by saying I am a smoker and i do think that is the issue however i just want to get a bit of advise before i dismiss this. Basically ive often had problems breathing all of a sudden out of nowhere i would get sharp pains in my chest. feels like a bubble for lack of a better word and though i may only be after inhaling or exhaling the tiniest amount it feels like if i breath out anymore or inhale any more somthing is going to pop. This was a regular thing and then i thought i found out what it was, i though it was something to do with my posture because after a while i noticed that once it happens if i really sit up straight and basically stretch my upper body it goes away almost instantly. However twice in the past two weeks this pain has come and i haven't been able to make it go away. It seems to just go away itself after a few minutes but stretching doesn't seem to make a bit of difference and it can be extremely painful and i feel like i can only inhale and exhale the tinest amount or literally soemthing is going to pop. I initially figured this was just to do with my posture but seeing as the last two times no matter what i did it didn't seem to go away. Should i get it checked out or is it something of nothing. The main reason i am asking is because i am broke and really cannot afford to pay the doctor 50euro to tell me i am fine. but on the same point i don't want to be a fool either