Sounds like he might be a bit impatient. If it's a position you're not in often, he needs to give you time to relax and loosen up a bit rather than just going for it. It's for your pleasure as well as his
Please avoid poppers, especially as you are on BP medication
Use lots of lubricant and relax - taking deep breaths helps
Get your partner to take his time and don't worry if it doesn't work on the first attempt, it can take several tries to get it right - try not to hurry things, it will work for you eventually
You or your partner might want to experiment by inserting a well lubed finger first, just to get your sphincter to relax and get used to the sensation
If it is your first time bottoming, you might experience some pain, although it should feel pleasurable too. Stay in control and get your partner to go at a pace that works for both of you
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