Yes, you can buy equipment for smart phones, like AliveCor, to trace your heart rhythm. An even simpler and cheaper (free) solution is to download a heart rate app which works as a pulse ox monitor. However, the latter can't register EKG, it can only determine if your heart rhythm is regular or not (but it can be effective to rule out palpitations/premature beats)
But I have to warn you. Checking your heart rhythm could very easily become an obsessive habit. Palpitations (as long as your heart is healthy) is something best left to itself. It really doesn't matter if your chest sensations are PACs/PVCs or muscle spasms. Neither is dangerous. You are saying you want to know for certain for peace of mind. From years of personal experience I can say that you won't necessarily find any peace of mind. The best way to find peace of mind is to leave your heart to itself. Trying to monitor or control the heart will only make the palpitations worse, or at least more noticeable.
I went down this path, like is_something_wrong mentions, I became obsessed. Then one day I worked myself right up to a ride in an ambulance. and it was all for nothing. I had to let it go and in the end, that knowledge only made my life worse, it did not improve it.
I see no value in this now. It took me 3 years to overcome the phobia I got for a high heart rate, part of which was because I help and read this board and I learned about things I was better off not knowing. The other part was the HRM I was looking at.
Then novmeber of 2014 I started walking, which led to some jogging. By the summer I was running 4-6 miles at a 8:30min/mile pace and the only thing holding me back was my legs. My cardio was as-fit as when I was 19, depsite now being 48 and through a ton of self-inflicted heart issues. *And* I worked my way up to that level WITHOUT a HRM. I refuse to use a HRM. I gauge my progress with pace and watts.
p.s., this all started with me having about 6,000 PVCs per day back in 2009. It was ruining my life. Things settled down eventually, and they still come and go. But I gave up on hyper monitoring it.
p.p.s., I just read your profile and like me you have anxiety and panic attacks. DON'T MONITOR YOUR HEART! turn back now. I went down that path, at around your age. No good can come from it. I had to address the root cause, which was controlling my anxiety. Where you are looking is where you are going to go. It's called target fixation. Start looking at positive things you can do to improve things.
Lots of things can cause these sensations. Get checked out by a cardiologist to find the cause. This said from a spouse of a fellow that had open heart surgery and has sense experienced heart rythem issues. Nothing to play around with no matter what your age.