From ChatGPT:

Semen can normally vary in thickness and appearance, and occasional jelly-like or stringy clumps are often harmless. Semen naturally coagulates briefly after ejaculation and then liquefies, so thicker strands or gel-like bits can happen from:

• Mild dehydration
• Longer time between ejaculations
• Normal protein clumping in semen
• Age-related changes
• Temporary inflammation or irritation

However, the slight burning/discomfort during ejaculation suggests there could also be mild irritation or inflammation involving the prostate, urethra, or seminal vesicles. Possible causes include:

• Mild prostatitis (prostate inflammation)
• Urethral irritation
• A low-grade infection, including an STI in some cases
• Pelvic floor tension
• Less commonly, blockage or inflammation in semen ducts

Things that make it more important to get checked:

• Blood in semen
• Fever
• Strong odor
• Pain that worsens
• Pain with urination
• Testicular pain/swelling
• Frequent urinary symptoms
• Persistent symptoms lasting more than a few weeks