my mother is driving me insane

I recently turned 18, today I made plans to go to planned parenthood to get birth control - mainly to see if it would help at all with my skin and try to regulate my period because it never comes consistently- and she lost her shit. many MANY months ago SHE was the one who brought it up that I take it for those two reasons, at the time I JUST started talking to my boyfriend. we were maybe two dates into our relationship l. mind you, this was probably like half a year ago. but anytime I ever bring it up, I'm being shady because my relationship with my boyfriend is more serious now. I was about to leave, but had just missed the walk in time so I didn't go. when I bumped into her in the living room, she was on my shit. I felt like she was mad at me but I didn't do anything? I answered her calmly and truthfully
"are you having sex?" no. "tell me the truth" I am telling you the truth, im not having sex. 
"does your boyfriend ask you to?" no. "does he talk about it at all?" we have, not often, but sometimes. "what does he say?" not much, mainly just you'll know when you're ready. 
"I don't want him pressuring you because he's a little older and I know he wants to have sex." (he's three years older) he doesn't pressure me (he really doesn't) and I'm sure he does (I know he does, but he doesn't pressure me about it) 
"and I'm sure he's not a virgin." I know he's not (I feel better that he isn't, this was someone knows what they're doing). "he could have an STD, there's a lot of different diseases that spread around." I know what STD's are, I asked him that a long time ago because I felt like as his girlfriend I deserved to know just in case, he doesn't, he gets tested every time he fights (he's a boxer) "he doesn't fight all the time, he hasn't fought in a while so he could've gotten one since then" the last time he had a fight and got tested was a few months ago, we were together then. "does he know you're a virgin?" yes. "what does he think about that?" he doesn't really care. 
"I don't want you to think you have to." I don't feel like I have to. "because you guys are together today and could be done next month" yea I know that's possible. "just because you do it with him doesn't mean you're going to be together forever." there's no guarantee that anyone's going to be together forever.
"I just don't think it's something you're ready for."
here's my deal, I feel like I AM. not even just in an emotional or mental way - I mean I'm being responsible. I made sure I graduated high school first so I only had to worry about school, I'm 18 so I'm older than the age of consent, I have asked him if he's been tested for any STD's, I have been trying to get birth control for myself and every time I bring it up she tries to make me feel guilty for it. like if you THINK I'm doing it wouldn't you WANT me to be on birth control? and if I were sneaking around and having sex behind your back, don't you think I would've went behind your back and gotten birth control months ago? (I didn't share this with her) but we both agree condoms are a must have. I feel like I am being responsible about this! am I justified to feel this way? she said she didn't want me to feel pressured to, but my boyfriend doesn't pressure me to do anything with him - it's her! she's pressuring me not to, it's not something I would actually even share with my mom, I feel like that's not any of her business, but if I'm feeling like I'm emotionally ready and she's telling me I'm not isn't SHE the one pressuring me to not make my own choices? am I not being responsible enough, am I being stupid? am I the one who's wrong?? can someone either confirm or deny that they think I'm trying to be as responsible as I think I'm being?