Assalamu alaikum I keep forgetting things in my prayer or more likely doubt it. Like I would say the Basmalah before reciting and I would start doubting or say the dua in rukoo and maybe when am in sajdah I will start feeling like I didn't say it. sometimes I tried to continue praying but I my heart will be tight and I feel scare like am doing something wrong. If I say I'll pray sujood sahw then I'll be praying it my every salah. I feel like I have a mental problem because sometimes I found myself praying a particular prayer more than five times like I would be starting over and over please help.
Alaikumassalam wa rahmatullah,
Sorry to read about your condition. It sounds like OCD (obsessive-compulsive disorder) and there are drugs that help with it, so I recommend seeing a doctor. The Prophet 
says:
When any one of you is in doubt about his prayer and he does Dot know how much he has prayed, three or four (rak'ahs). he should cast aside his doubt and base his prayer on what he is sure of. then perform two prostrations before giving salutations. If he has prayed five rak'ahs, they will make his prayer an even number for him, and if he has prayed exactly four, they will be humiliation for the devil. (Sahih Muslim 571 a)
If you are not sure whether you made a mistake or not, then try to continue the prayer and cast away your doubts. At the end perform the sujud al-sahu just to be sure. You can do this with every prayer if you have to, there is no issue with doing it every time.
Best wishes.