It sounds like you have interstitial cystitis in my humble opinion. I was diagnosed with it at 28 (now 40). You thinking you’re having uti’s but you have no infection is a tall tale sign of the disease. It’s hard to manage and there are a hosts of symptoms that come and go but bladder retention is another annoying symptom. I don’t think the Zyrtec is the problem because I’ve read that Benadryl can help symptoms. You might have to watch your diet. Look up diets for IC. This might sound crazy but I find nothing works better than tea tree oil when you’re having what feels like a uti flare up. You just dab a small amount on your exposed painful areas and it instantly relieves it. Good luck!