Take them together. The amounts are small enough that they are not going to really interfere with each other.
Calcium and magnesium are generally taken together. The only time they are taken apart from each other is in cases where high calcium is causing problems such as high blood pressure, spasms, restless leg syndrome, spastic bladder, etc. Even with these it is generally just extra magnesium taken separately. Unless the person has high serum calcium from a conditions such as hyperparathyroidism they can take the calcium and magnesium together, preferably before bed to help with sleep and take extra magnesium by itself the rest of the day.
Have you tried the bioflavonoid quercetin for the histadelia? Quercetin is a strong, safe antihistamine. I recommend 500mg of straight quercetin, not the QBC, 3 times daily before meals.