Swollen Penis Tip & Scratchy Anus

Hello, I have a swollen penis tip which sometimes feels numb and a scratchy anus. Its been on and off for 3 months. I have had a few STI checks which came back negative. I have been back to the sexual health clinic a further two times and also been to the doctor. They have given me Canestan which i have tried on my back passage and penis which hasnt worked. I have been told its nothing and leave it. I dont know what else to do? The last time i went to the Dr they gave me a hemroid cream even though it wasnt hemriods and told me to go back to the sexual health clinic. I am diabetic, i dont know if that makes a difference. Please someone give me some ideas or suggestions, its making me so miserable....