How old are you?
How do you feel when your HR is at 150 bpm and how long can you sustain activity at this bpm level before you need recovery time?
The BP medicine can impact your HR readings. Out of curiosity, do you know your resting HR - the bpm when you first wake up in the morning and do anything? If you don't know that reading, then how about when you are sitting down and as calm as can be?
Who is telling you that you are working your heart too hard. Your description of what you are doing is indicative of someone who is attuned to his HR and that is good.
I think HR monitor training will help you improve your fitness and make progress in
weight loss tremendously. You've got to work the nutrition department though and be prepared to make your transformation a long-term, lifetime journey.
Why don't you post your workouts in the online
journal section of this forum. You'll get lots of good feedback by people here who are interested in your success. And you'll have lots of people privately cheering for you.