You can as well use si in the past. Try saying "I was making myself bad" or as it is "I was becoming bad":
1 translation: I was becoming bad.
2 translation: We were having a conversation.
Same for future. Say:
3 translation: We will be having a conversation.
Good. Here is one rule which actually simplifies the usage of si.
Anything put at the beginning of the word (be it pa, ne or whatever) attracts si just right after itself.
That’s quite like a magnet. For example, they are having a conversation would be jie kalbasi but if you made it into they are not having a conversation you use ne and it attracts si so it becomes jie nesikalba.
Whenever si gets attracted, it stops doing all the other things it used to do: it does not put that e or o separator, it does not get contracted to s, it’s always this plain simple si.
Use it in a few sentences:
4 translation: I am not becoming bad.
5 translation: We were not having a conversation.
Just like ne, pa also attracts si.
Let’s have an example of usage of pa. What is?
6 translation: To be saying
7 translation: To say
How would you say to say oneself:
8 translation: To say by oneself
This to say oneself actually implies that you say yourself, talk yourself out, you say what’s inside you, in other words, you have a say - it’s a bit of an idiom in Lithuanian, too. So, how would you say:
9 translation: I want to have a say.
You could also use padaryti instead of daryti to mean to make (or ir could mean to do) instead of to be making (or to be doing as we have learnt). How would you say:
10 translation: I became good.
Attention how you didn’t say I was becoming good but you said I became good with completion.
Combine both pa and ne (ne comes first) and say:
11 translation: I will not become bad.
Of coure, not only pa and ne attract si: whatever you put in the beginning does!
So here it is. Plain and simple.