Blood pressure is a measurement of the force applied against the walls of the arteries as the heart pumps blood through the body. The pressure is determined by the force and amount of blood pumped and the size and flexibility of the arteries.
Your pulse is different. It measures 4 things:
1) the number of times your heart beats per minute.
2) the rythym of the heart
3) the strength of the beat
4) the hardness/softness of the arteries
Your blood pressure isn't low. It's considered low when 2 things occur:
1) it's below 90/60
2) if blood pressure changes from the baseline or normal condition. A fall of 30 mmHg or more from a person's normal baseline is considered low blood pressure.
A normal pulse range is 60 to 80 beats per minute while at rest. It changes constantly with the amount of activity, both mental and physical. A sustained pulse at over or near 100 at rest is considered to be tachycardia.
My blood pressure is usually 107/60. Sometimes it's 98/57 and my pulse will be around 88 or something. Some people have low blood pressure with fast pulses, and it's normal, sometimes it's not. Ask your doctor just to be sure.