There are only three possible sources - your own physiology, God / angel or devil / demon.
I think you could probably discern if it was due to your own body, and you've most likely dismissed it. In other words, I doubt if you think it's a health issue.
That leaves the other two. If it's God, I think He's probably waiting to see if you persevere with your spiritual growth despite the discouragement, or whether you're going to give up and relapse.
If it's the devil, it's discouragement, pure and simple.
So about all you can do is persevere, regardless of the source.
That said, in the past I've had demonic attacks at night (usually) and part of that has been something like a heavy weight pressing down on my chest. But it doesn't last long - I suspect another spiritual being pushes them off again, and tells them to shove off.
I've also had from time to time what you might call a "heartache" feeling, which usually indicates to me there's trouble somewhere, but most of the time I don't know who, where, when, what or why. All I know is that there's trouble brewing. As a psychiatrist (a highly spiritual Catholic psychiatrist) commented to me, these spiritual "messages" are always vague, in the sense you're never quite sure what you're being told.
I had a prophetic pastor who was uncannily accurate, but even he used to preface his remarks and propecies / predictions with "It seems to me that..." or "I think He's telling me that..." He was hedging his bets.
On one occasion, he was going on with all these negative things he thought I'd do in the future. But then he suddenly stopped, and said "Hang on a minute! I think the devil's telling me all this!" Even a good and holy man like him could be temporarily deceived.
In your case though, I think you just need to persevere, and not lose heart.