I agree, core work will help, plus what worked for me also were walking lunges and squats, loads of them. I've mainly had achilles problems rather than upper leg problems, but would occasionally have to take time off for thigh strains, including one where I seemed to be able to feel all the vibrations going up my femoral shaft while running.
With that last one, I rested for a month or so, then started adding in walking lunges while walking round my usual running route, and standing squats. Six months on, my upper legs now feel very steely and I am running three of four 10k distances every week, with no twinges whatsoever.
My legs weren't conditioned properly before - when I started doing the walking lunges I could feel a massive burn on the inside of the thighs after doing 10 or 20 lunges, and I was wobbling while doing them - now they're pretty easy. My adductor muscles in particular have got much bigger, which is bad news as my suit trousers will now go threadbare on the inside top of the leg where my legs rub against each other. Glutes have also got harder.
I feel more confident about avoiding groin/upper leg injures now - good luck.
If there's no swelling then it doesn't sound sound acute so ice probably won't help (but I'm not a physio).
Give it a few days rest, then before the next run try heating up the achilles/soleus with a gel pack before running - when I had a similar stiffness recently, usually my lower leg used to stiffen up at the start of a run and then stay stiff, but if it was warmed up beforehand it wouldn't ever develop to be too stiff over the course of a run. For me, over about ten or fifteen runs eventually the problem went away, as I guess the achilles wasn't placed under so much stress at the start of a run (cumulative benefit). I run about 30 miles per week.
Echoing the above, foam roller on the soleus (do all round it, back and both sides) and as Paul says, plant your foot on the floor and bend the knee - do this as many times a day as you can to keep things flexed up. And eccentric calf stretches, but go easy on them when you start - I did 3 sets of 15 with bent leg and 3 sets of 15 straight leg when doing my achilles rehab, and my soleus locked up in my right leg straight away, so start gradually.
Also, shoes may have something to do with it - I have some Asics GT-2170 shoes where my heel feels like it sits slightly below my midfoot, when I run in those (if I run without a heel insert) my soleus stiffens after about 3 or 4 runs (but the first couple of runs are very comfortable due to the overall good cushioning). When I run in my other Brooks shoes, my heel sits further up and there is less midfoot cushioning/thickness leading to a bigger 'heel to toe drop', and after a few runs in those my soleus stiffness goes away again. But all that maybe specific to me.
I have GT 2170s and have Sorbothane heel inserts in (small ones just for the heel part only, not reaching to midfoot) - I have no problems with stability and my footfall feels solid and stable (landing midfoot, more or less).
Are your Orthaheels the full length blue sports ones with the firm arch support? I have the full length blue ones from a while back when I used them with my old shoes - I just put them in my GT2170s and they didn't feel right at all, they pushed my feet upwards and outwards and made me feel bandy legged. But it depends on the shape of your feet I suppose, they might be ok with you. The person in the Asics store assessed the GT2170s as being ideal for me, so using the Orthaheels with these would change my running style too much. The heel cushioning feels fairly minimal (though mine might have got impacted down by now) so I think that would be ok (if they replace the original somes rather than on top of them).