I'm sorry you're having these life difficulties.
I ended up catching a cold. Didn’t go to work for a week.
Assuming your work schedule puts you in the workplace 5 days a week, I think you calling out is having the negative impact you're seeing, not because you haven't completed the PSI Seminars. Unless you have other health conditions complicating a cold, being out for 5 days for a cold feels excessive. A day? Sure, no problem. Two days? Probably okay. Three days? Borderline at best. Four days? Employer would be asking "what kind of cold is this?". Five days (which likely bled into 2 more days for the weekend). "I'm not sure we can rely on this person going forward".
Again, if you've got other health issues where a cold is a much bigger deal (such as being Immunocompromised, as just one example) then 5 days out for a cold could be entirely reasonable. However, those challenges (and requests for accommodation) need to happen when you're hired, and not after-the-fact when you've had a 5 day absence.
I know I have no future there. And when this internship ends, I will not have an income stream from an additional source.
Since you posted in "Advice", I assume that's what you're looking for. My advice would be to reach out to your manager and take responsibility. Let them know that you're still learning and that even if it means you don't have a future with that employer, its important for you to learn and any actions or advice your manager would have for you would be welcome even if it is critical of you. If they say things you don't like to hear, be courteous, be professional. Thank them for being honest with you and let them know you're committed to learning from this and that you're receiving their criticism constructively.
Good luck!