I suspect blood vessel spasms to be responsible for this, but I could be wrong. Have you asked your LLMD about this?
If I were you, I'd be careful with Magnesium - too much Magnesium can lead to low blood pressure and heart rhythm disturbance. Best is to supplement both Calcium and Magnesium, that way the two minerals can be kept in an appropriate balance with each other and this reduces the chances for side-effects. The usual recommended ratio for Calcium to Magnesium is 2:1 (for example, 1000mg Calcium and 500mg Magnesium), but you may need to experiment with it a little - some find they need more Magnesium than this relative to the Calcium. Also it is best to take Calcium and Magnesium in divided doses throughout the day for better absorption.
Chronic Lyme Disease, Gluten & Sulfite Sensitivity, Many Food/Inhalant/Medication Allergies & Intolerances, Asthma, Gut issues (dysmotility, non-specific inflammation), UCTD ("Secondary Lupus-Like Syndrome"), Osteoporosis, Anemia, Lymphopenia, intermittant Pancytopenia, chronic malabsorption/malnutrition, etc.; G Tube; Currently TPN-dependent.
Meds: Zofran, Pulmicort, Heparin (to flush PICC line), IV Cipro (for G-tube site infection).