Is losartan the only best medicine for heart failure and kidneys improvement ? if a person is allergic is it really a shame ?

No and no: There are many options to replace losartan and a detailed discussion with treating cardiologist should clarify options. If a drug is not tolerated is understandable and it is never the patient's fault/shame, relatively commonly seen in practice.

Losartan CHF: No. There are many good meds for CHF. Some are allergic to some and some are allergic to others. Diet also plays a key role. Go to uptodate.com and read more. Curious you have heart failure at your age.