It sounds like you are in a challenging and emotionally complex situation. It's understandable to feel anxious when your desires for the future, especially regarding marriage and children, aren't aligning with your boyfriend's outlook. Here are some steps and considerations that might help you navigate this situation:
1. Reflect on Your Priorities
Start by taking some time to reflect on what you truly want for your future. Make a list of your priorities regarding marriage, children, career, and financial stability. Consider how these priorities align with your biological realities, especially given your health concerns with endometriosis.
2. Have an Open and Honest Conversation
It seems that you have already initiated some discussions, but it may help to have a more structured conversation. You could express your feelings clearly, using "I" statements to avoid sounding accusatory. For example:
"I feel anxious when I think about our future because I have a strong desire for marriage and children." 
"I want to understand your perspective better, as my biological clock is a concern for me." 
Be specific about your concerns and how his shifting timeline impacts your feelings and plans.
3. Assess His Response
Pay attention to how he responds to your conversation. Is he willing to discuss your future in more detail? Does he show understanding and empathy toward your concerns? A lack of willingness to engage in these discussions may indicate a deeper issue regarding his commitment.
4. Consider the Financial Aspect
While financial stability is important, it shouldn't be the only deciding factor for starting a family. Many couples find ways to navigate financial challenges together. Talk about your thoughts on balancing financial readiness with personal desires for family and marriage. For instance, you might say:
"I understand wanting to be financially secure, but I believe we can make it work even if things aren’t perfect." 
5. Evaluate the Relationship's Foundation
Consider the overall health of your relationship. While you mention no major issues, the communication gap is significant. Ask yourself:
Do you feel heard and valued in the relationship?
Is he willing to work on communication to meet your emotional needs?
6. Set a Timeline for Yourself
Given your health situation, it might be beneficial to set a personal timeline for yourself regarding major life decisions. This could involve giving your boyfriend a certain period to become more certain about his feelings regarding marriage and children. For example, you could say:
"I need to make a decision about my future within the next six months based on our conversations." 
7. Seek Support
Consider talking to a therapist or counselor, either individually or as a couple. A professional can help facilitate discussions about your future and provide insights into any underlying issues that might not be immediately apparent.
8. Be Prepared for Any Outcome
Ultimately, you need to prioritize your own well-being and future. If your boyfriend continues to be non-committal and you feel your needs are not being met, you may need to contemplate whether staying in the relationship is the best choice for you. It’s important to remember that:
Your happiness and future family are worth fighting for.
It's okay to walk away if your partner cannot meet your core needs.
Conclusion
This is not an easy situation, and it requires careful thought and consideration. You deserve clarity and commitment in your relationship, especially concerning such significant life decisions. By communicating openly, setting clear expectations, and considering your own needs, you can make an informed decision about your future.