This could be long and rambling so bear with me!

Izzy 4 and half months (almost). From 6 weeks she was sleeping from 7 at night for up to 6 hours and from 8 weeks she was sleeping anywhere from 8-11 hours a night - increasing as she got older. She was self settling for her day sleeps as well, sleeping for one hour and up for an hour and a half. The only time she would feed to sleep would occasionally be her 7pm before bed feed.
Until she hit 3 months.

Since then it has become progressively worse - she is waking up to 3 times a night to feed most nights(goes straight back to sleep thank goodness) and most day sleeps - she simply will not self settle, she will cry until I feed her to sleep. Today I tried comforting, patting, singing for 30 mins and she just ended up on the boob again - mainly because I can see how damn tired she is and just want her to get a rest.
Normally at night she will feed and go to bed no worries, the last few nights have been sketchy and then last night it took one hour to settle her - shes never been like this since she was born.

Her feeding has become erratic - often kicking, scratching etc and not feeding all that well -Ive stopped persisting with that though and just try again in half an hour. (I wonder if she is getting alot at night and therefore doesnt need it during the day?)
So a few questions

1# I still have her in a up for hour and a half then nap routine - should she be up for longer now that she is older?

2# How many hours between feeds should I be up to now?? I thought 3 hours - she occasionally will make it that long but recently its been every hour and a half to 2 hours which I mentally and physically cant sustain. (although some of those have been those muck around feeds I mentioned.)

3# Shes generally also been very clingy - so I wonder about separation anxiety too - although I really think its too early for that. Could it all be related to her lack of routine and pattern recently?

4# Teeth? I cant feel anything, although she gets the pink cheeks every few days for an hour or so and drools alot (what baby doesnt?) If so what can I do to help?

Can you tell Im just about beside myself with what to do?? Ive got tears running down my face because I have a million questions in my head and wonder if Im doing something wrong that has thrown this little angel for a loop. (Also the control freak in me that wants to fix it now , yes I still have my sense of humour through the tears!)

Any advice or stories of experience would really help right now.