Here another link for you
http://dicesites.com/tools and from the sites you can check that the probability to get 20x loss streak is about 0.00011637% . The number is close to zero but it is not impossible so with that being said, conclusion is that you are unlucky to have 20 + loss streak
More generally, the probablility that any set of rolls go a particular way is just the multiplication of the probabilities. This also makes intuitive sense. If you have one roll at 50/50 there's a .5 chance, but when you want two rolls at 50/50 on a particular outcome for each roll, consider with coins and H, T:
HH
HT
TT
HT
Those are the four possibilities, so getting any particulare one is a 25% chance, that is, .5*.5. The patten continues with 3 rolls, there are 8 possible outcome sequences and the probabilitiy for any paritcular outcome sequence is .5*.5*.5 (ie, 12.5%).
If you want 20x, it's .495^20. This is indeed a small number if you only roll 20 times then the chance that you guess the outcome of all 20 rolls in sequence is very small. But if you roll 20 times, then another 20 times, you just doubled your chance. If you roll a million times, it's another story. So, you have to consider how many times you rolled if you want to decide whether any particular streak of 20 is "lucky" or "unlucky".