especially in morning I feel very dizzy and tired

I'm 23/F overweight, normally have low BP (around 100/70) at times shoots up to 140-150. At times, especially in morning(sometimes after any outing also), I feel very dizzy and tired; sometimes I experience slight muscle pain also. It often fades after noon. This has been going on around for the past 10 months. Never met a doctor regarding this until yesterday. He said my BP was 149 then and asked me to reduce my salt intake. I'm somebody who basically uses less salt and does not get stressed easily. Since I knew that normally my BP is low, I got confused. Today evening when I checked again, it was 100/70, around the normal BP for me. Please help. Is this normal?