Well, good on you for having a go, but how exactly are you doing it? Are you listening bar by bar and finding the notes by ear, or are you following some kind of music - as in written down notes?
There are only a few ways of learning really, and so much depends on your temper - how long before you walk away in disgust.
Some people learn by learning to read music and they play exactly what the book says. Other people never learn that way at all and have a musical 'ear' so can identify the root note of every chord, or read it off a piece of music by looking at the chord symbols - so if the chord is C, they play a C, or of the chord is written as say, G/B then the chord is G, but you play a B in the bass.
If you do that, AND you listen hard you will find that bass music of almost any style has little habits - habits that work to connect chords. If the chord is C, then a bass line might alternate between C and G, C on the first beat, then G for beat 3 of the bar. Sometimes the C above will be played, but that C to G works for the chord of C, and then if the C changes to an F, then the bass might focus on F and Bb. Then - if the music is about to go from C to the F chord, the Bass note much walk up from C to the F by playing C-D-E-F, just before the chord change.
Of course the rhythm the bass plays is also important so it could go bum-bum-bum-bum - for notes in the bar, or just two longer ones, bum (for two beats) then another bum for the final two beats. Then the rhythms get cleverer. bum-dibum, bum-dibum or even bum di bum-didi-bum. To see how bass lines work. Have a listen to the final countdown. First listen the bass is wild, but second listen you'll discover the secret is the rhythm, there are actually very few different notes. Have a listen to the bass in Gary Moores tracks - things like still got the blues for you - it's easy to pick out what is being played.
If you have a good ear, you'll spot the common little phrases that get simply joined up.
RE: HEY JUDE - Are you counting at the right tempo? It's about 70bpm or so isn't it, so where is the bit you are getting stuck? I'm guessing its actually 16? Bar 1 starts hey Jude, don't get it - and bar two starts with bad. At 'any time you feel the pain, it first changes and then starts a descending bass line - with some less common notes that then gets repeated till it starts going down again - then we're back to the original verse line.
Tell us what you're stuck with. If you want - post a short clip of you playing so we can guide further.
So much depends on how best you play.