If there are some differencies in these sentences, please, explain it. I think all versions are interchangeable in this context. Only the last one means that the end result will be negative, isn't it? There is an indefinite end result in other sentences.
I have difficulties with physics, chemistry and maths.
I have problems with physics, chemistry and maths.
I have troubles with physics, chemistry and maths.
I am struggling with physics, chemistry and maths.
Best Answer
As Felinius said, the phrases aren't completely interchangeable. You could order them based on their relative strength, and I'd say, from softest to strongest:
I don't believe the last one implies the result will be negative, but it seems to indicate the most dire situation. I'll say that "struggling" sounds very much like they are trying hard, though the others don't invoke the same feeling.