A part of what you are going through is of course, age. At 19, very few women know what they like. The misconception of “bigger is better” is a cultural thing, at least here in the US. It’s a superficial one, but a reality. I don’t think any of the girls I knew at that age had even had an orgasm, let alone an orgasm plus a genuine connection.
Physically speaking, most women do not orgasm from straight penetration (not to mention as women age, they produce less moisture, so straight penetration can be uncomfortable without a warmup to get the “juices flowing”). Focussing on what your partner really likes is key to achieving orgasm. Most of the nerve endings in the vagina are only a few inches in, and while it is a muscle that stretches to fit both large penises and babies, the “rearranging of someone’s guts” will hurt.
Larger penises can cause harm in a number of ways, including cervical bruising or damage, overworked muscles, dyspareunia, vaginismus, and much more. While they can be temporary fun, your vagina will feel it in the morning, and if it’s a long-term partner, it can result in frequent sex being off the table.
As far as “average size” I cannot tell you, as I don’t have one. But I can advise you, continue to focus on learning the oral, focus on clitoral stimulation when fingering, and become comfortable with yourself and your size goes way further than a larger member.
Plus women are more likely to say yes to anal with average or less penises.