Is the Cal-Mag your taking liquid? My surgeon recommend a liquid because it is absorbed better. The brand he recommended and that I have been taking is Lifetime Liquid Calcium Citrate. Each tablespoons contains 600 mg calcium, 400 mg Vit D, & 300 mg Magnesium. I started by taking this twice/day, but after blood tests needed to increase it to three times/day. So, in total I now take 1800 mg calcium, 1200 mg Vit D, & 900 mg Magnesium. I also take an additional 1000 mg Vit D on top of what is included in my calcium.
I don't know if you are aware that in addition to getting your blood calcium levels checked, you also need to get your PTH (parathyroid hormone) levels checked at the same time. The reason for this is that your blood calicum level could be in the normal range, but if your PTH levels are high it means that your body is stealing calcium from your bones to keep your blood calcium levels in the normal range. This was how we discovered that I was not taking sufficient calcium.
The Lifetime Liquid Calcium Citrate is available in most health food stores and it runs between $16 – $17/bottle. Each bottle contains 32 doses. I buy mine online from VitaCost, because each bottle is between $ 7 – $ 8/bottle. It comes from the US, but even after I pay for shipping and taxes it runs me about $ 10 – $ 11/bottle, and it comes usually within 7 sevens of being shipped.
Your advice about getting a base line bone density test is good – especially for those of us over 50. My GP had me get one done the first year following surgery and we will do a follow up in three years.