If you're going all out hard on each run, that could be why. Running more miles and running slower will make you faster. 80/20 Running by Matt Fitzgerald is a good book on this. If you're already running slow, then I'm not sure.

What Austin said.

What do your runs look like?

I run nearly every day, for a tri focus it would be almost ALL easy. It's a different beast for a 10k focus...but still 6 days a week.

You do need to build into it, though. Which means dividing your average weekly mileage by the new quantity of runs. If you try and go from 2x 10 miles to 4x10miles... You're gonna take a hit. Keep your weekly miles constant. Then once you adjust to the higher frequency (a couple weeks) build the mileage up.

This is normal. Believe or not, you are NOT getting slower at running, you are getting faster. It's just that the accumulated fatigue from the added load is masking it and your paces thus go down.

Trust me, if you have added significant volume, then later on take a taper, you'll really feel the jets.