Not everyone can expect to study at the same intensity and with the same degree of success every uni year - or even between every unit.
There are so many things that affect how you go, and a father who is blind to this and keeps expecting peak performance no matter what is not a help, he just emphasizes in such a way as any thing else is seen as failure, rather than learning and coping with the downsides of life.
You have a couple of things that may well have affected you more deeply than you realise, the first being the anniversary of your brother's death near the start of the academic year, and secondly your friendships.
You have found that going to uni and people drawing apart is not uncommon, and even though you have been a supporter person, at your emotional expense, you are not getting the same in return.
The units you have to do at the moment may not be interesting, or rely upon skills in areas where you are weak (this applies to everyone). Sadly one fail can lead to more, a sort of loop where discouragement in the first leads to disillusionment and lack of confidence, and round and round it goes.
OK, so what to do? This may seem to be unrelated but I'd have a physical and mental assessment by your GP, there may well be something there that requires medical support.
Secondly I'd visit your lectures and tutors and see if you can work out where you are going wrong, if lack of concentration then a study group can be a real asset, where not only is the pace set for you , but by interaction you both lean and teach. It can also be a place where new friendships are formed.
Uni Councilors are also good peple to talk with, they can be very helpful, for example if you are running late, and may have their own suggestions.
Not getting enough marks is a challenge, not only in the unit, but it can help you with all areas of life as you learn to cope and adapt. There will always be problems that have to be dealt with.
Remember if in year one you were very capable of the study that ability is still there inside of you and only needs to be brought out -you can get there.
Please come back and say how you are going