bpt — It seems you are bringing up a completely different (and I believe valid) point — that people may be making choices regarding having children due to peer pressure. (And by the way, it goes both ways as well — I know of people who have children close together and have gotten comments such as “I can recommend a Posek for you to speak to if you want. . .”) If you wish to open a discussion on this topic, by all means start a thread. To raise it in this thread, where the OP is expressing pain at his inability to make that choice seems to me to be highly insensitive.
This is particularly so when prefaced by your first post which dismissed the whole concept of secondary infertility and accused those who feel pain over their situation (including the OP) as being “selfish”. You did this by setting up a “straw horse”, and putting words into his mouth that he didn’t say. (“I think it is very selfish for someone with one or two children to equate themselves with someone who (loi uhlainu) has no children.” — The OP clearly did NOT equate themselves with someone with no children — he even specified that his awareness of those suffering with no children makes him doubt his own pain!) Perhaps you object to the use of the term “infertility”, which in your mind means no children. Infertility however is a medical term referring to a medical condition that prevents one from having kids. Both primary and secondary infertility are medical diagnoses.
Finally, I don’t quite understand your comment with regard to the first 2 children. I would hope that no parent is having constant discussions with their older children with regard to their desire for more children. How are they sending this “unintended message”? By davening? By having treatments which I would assume the kids are not told about? The families I know are certainly not walking around talking about it with their kids — unless the kids bring it up, which is often the case. Additionally, where do you see in the OP’s post (or in my description of my relative for that matter) that anyone feels that “they have achieved nothing” by not having more kids? Each child is a complete world, not to mention that the people I know (and I assume the OP as well) have achieved much in many other arenas of avodas Hashem as well. That doesn’t change the fact that one can legitimately desire more children and be pained if circumstances beyond their control prevent it. It seems you are projecting your own negative social experiences, and perhaps the feelings you think others have towards you, onto a whole class of people in a very unfair way.
Personally, my mother had complications when my youngest sibling was born that prevented her from having any other children (there were no treatment options available for the situation, so she knew it was over). It wasn’t till I was an adult that I realized what pain she must have felt when she knew at the age of 31 that she would never be able to have another child. She never expressed that pain to me, however, and the only discussion I remember with regard to it was one time when I was innocently commenting (for probably the hundredth time!) about “when we get another baby. . .”, and my mother explained to me that because of how sick she was after — was born her body is not able to have any more children. I certainly felt disappointment — but for myself, not for her!