Brief Answer:
I would like you to be evaluated further...

Detailed Answer:
Hi,

1. Does the pain improve when you move your legs?
Aching pain in lower limbs especially at night once you go to bed is reported by people suffering with restless leg syndrome. This pain improves with movements. If you feel better by moving your legs, then you might be an individual suffering with restless legs.

2. Achy legs at night have been reported by a small group of people on atenolol. From the details provided the indication for atenolol is not very clear. Perhaps you are on it for treating hypertension - you can discuss with your doctor and plan alternative medications - may be increase coversyl or add ARB inhibitors.

3. Premarin, an estrogen conjugate is associated with deep venous thrombosis (DVT). Calf pain/tenderness along with swelling are classical symptoms of DVT. Though you do not seem to be suffering with this complication, if I were to be your treating doctor, I would definitely consider this as a possibility.

4. Lipitor - this is a drug used that is used to lower lipid levels. Muscle aches is again a reported side effect. Elevated CPK and LDH are seen in some cases of lipitor associated muscle aches.

5. Lastly, yes calcium and magnessium deficiency can cause night cramps; magnesium and calcium supplements is beneficial.

In brief, If you were my patients, I would consider the following three treatments:
i) Order Serum CPK and LDH. If the calf is tender and appears swollen, I would also write for Doppler scan of lower limbs
ii) Revise your medicines especially the blood pressure drugs. Perhaps will also add Co-enzyme Q supplements one table a day. (Premarin would be stopped if features suggest DVT). I would also encourage you to continue magnesium supplements.
iii) If the symptoms doesn't improve, I would refer you to a neurologist for restless leg syndrome and neuropathy evaluation.

Hope this helps. Let me know if you need clarifications.

Regards