Fatigue after changing bike type? My hardtail MTB was stolen. As a result I started looking for a new bike.

After much research, I realized that most of the biking I have been interested in over the last few years seems to fit the bill for this newfangled thing they are calling a gravel bike.

So I got a Specialized Diverge Comp E5 with Future Shock. I am riding in a new posture and for the first time in my life attempting to ride the drop-handlebar posture as I have never ridden a road bike or anything like it. 

I have much to write about this machine, and my experience of it, but for this post suffice to say the following:


I am amazed how different everything is. It's like learning to ride all over again. I feel either exhilarated or terrified most of the time, the latter especially downhill over MTB type stony terrain.
The bike fit is not yet right. I need to tune it. But it is not very off.
After doing even short rides on asphalt/tarmac/paving, say to the tune of 30km, I am absolutely knackered. 2 days on my thighs are killing me.


Is this normal for switching bike types? I was planning a longer trip in the next few days but right now I don't have the confidence. I think I may have to delay as everything seems so shockingly different and  my body is in permanent tension. What should I expect in this situation?
It's entirely plausible that you are experiencing muscle pain and fatigue on a bike with a substantially different and more aggressive riding position. 

If riding on the drops is very unfamiliar and difficult, try riding on the hoods most of the time and switching to the tops to get a different hand position occasionally. (A lot of riders spend most of their time on the hoods rather than the drops.)