Frequent urination and weight loss. Me.

I had a problem of frequent urination in 2018, multiple tests like sugar, ultrasound and blood tests were there but nothing was found. I got habituated with that and later it subsided, but recently since few months i have seen the same kind of frequent urination will happen and i will also lose weight during that time, i checked pre post sugar they were normal as well as hba1c was normal. I dnt have uti as well, but sometimes while sitting on chair i felt a tingly sensation in my urethra, for 1-2 seconds. I am scared if this is any autoimmune disease or something. Also I struggle to gain weight, my height is 5'7 and i eat a lot as my target is 70kg but i am falling down to 66.9, 67.1 etc.. please help me.