I have been primal for going on 3 weeks now.

I started by exercise regime at the same time. Which includes MWF lift something heavy for about 30 min(usually targeting 2 areas a day ex. yesterday was abs and arms 3 circuits of 12-15 reps).
And TU/TH just cardio usually 30-45 min(depending on how i feel) of elliptical.
as well as swimming about 2-3 days a week for fun and for cardio/fitness(ex competitive swimmer and current lifeguard).

The past 2 weeks for cardio it has been the elliptical as a choice of cardio. I have always liked it and its fairly easy for me to get a good workout in. Until it started getting difficult to get my heart rate up (past 140) and I had to push myself harder. And I know in swimming when that happened it meant that my body had become adapted and was being the most efficient it could be. So I would switch it up and work on a less preferred stroke for a week or 2 then go back and I would be good.

So on Monday I switched to a "learn to run" 8 week at home program. Consisting of slowly increasing your time running so you get the stamina to run for 5km at the end of a 8 week program. COOL.(Because I am a swimmer and a bicycler so run is all i need to achieve my goal of doing a triathlon one day)
So I am on walk 2 run 1 for 30 min with a 5 min cool down followed by tons of stretching(because I am NOT a runner AND FEEL it everywhere!)

My issue is that my eating habits have not changed. I eat after my AM workouts.Daily macros are about 40F/50P/10C BUT....This week(yesterday and today) I am absolutely EXHAUSTED after my workout...Not during but after. I get home and I don't want to even shower. I feel like I cant even eat.(But i do).I sit down for a second and I pretty much feel like I need to lye down and nap!!(I never nap!!)

im F/25/220 with 125LMM, very muscular and athletic and always active.

Does anyone have insight as to why I am feeling this way?
Am I just exhausting my body because I am not a runner?

Thanks to all who read and reply!