"I sent a renewal request during the summer, but I've had no answer yet, is it normal?"
The sous-préfecture is currently processing the requests sent during the summer. You may have received an "attestation de prolongation". It certifies that you have the right to remain in France, while your file is being processed. It is a valid residence permit for all your formalities (CAF, CPAM...).
HOWEVER, if your request was sent too late (less than 2 months before your permit's expiry date), you will not receive an attestation de prolongation. Check your ANEF account regularly to be on top of any document request made by the sous-préfecture, as your file will still be processed.
Once the sous-préfecture has approved your request, you receive an "attestation de décision favorable".
If you've sent your request on time but have not received a "prolongation" or a request for documents, send us your proof of renewal request by email at etudiant@cmibrest.fr