The only way I can run in the evening is to do it straight after work and before I get home. I take running gear to work and change before I leave, drive to where the kids are in after school club, run, then collect the kids. If I go home, or in particular if I sit down on the sofa, then all is lost. I also run in the evening when the kids are in a karate class. I have to be there anyway and it's pretty dull sitting watching. It's an hour long, so that gives me time for a run followed by a shower in the sports centre where karate is happening.
It's the margin of error on the device that I'm thinking of though. I'm trying to run 3 times a week, one of which is Parkrun. The other 2 runs I run 5k as measured by my phone and I believe it but then do I compare that time with what my phone measures as 5k of the Parkrun or do I compare it to the whole Parkrun. I know, it doesn't really matter...
I agree with others, that with those symptoms, you HAVE to go see your GP.
However, if the GP is happy you're okay, then it probably is just a question of slowing down even more on the runs or running for shorter periods.
I know you say you can walk almost as fast, but running is a different action and is more tiring than walking even at the same pace. If you can't carry out a conversation whilst running (even a breathless, slightly incoherent one counts) and you are exhausted afterwards, then you are clearly working harder than you think
You say you are a little overweight. As someone who is more than a little overweight, don't underestimate the effect that can have on your ability to run. However overweight you are, imagine that weight on your back in a rucksack (this is what I am currently repeatedly telling myself and every little bit off is going to help!).
And if it is just overweight/ lack of fitness, then the good news is it will get better. Just stick at it.
But please see your GP and get it confirmed that that is all it is.
No, it won't break the diet plan, and I don't eat all the calories back (but I generally eat some of them) - it just gives me a bit of leeway. Overall it doesn't really matter, I just want to know how far I've run and how fast. In the great scheme of things, it doesn't matter a button, I'd just like to know. Because I'm an obsessive control freak (until I get bored)...And I don't know whether I'm overestimating how far I'm running on other days, underestimating on Parkrun days, or possibly neither as the non-Parkrun routes I run have much less tree cover.