As to abnormal wake times, I know what you mean :lol: . My dd has always been like this. Through her first year, she was always waking at different times, anything between 6 am and 9 am. I tried to wake her up in the morning at 8 am but decided it wasn't working for us either. First of all, she hates being awaken and sometimes just slept through my attempts of waking her, sometimes was so grumpy, she didn't obviously get enough rest. So I decided to go with a flow. Because of this erratic wakings our days also didn't have the same pattern every day.
To make things worse, she was not consistent with her naps, for example if she woke up early, one would assume she would go earlier for her nap... WRONG. She actually went later. On the days she slept longer, her nap was earlier than "usual".
The only thing that helped was knowing her awake times. For example, at some point she was able to go 2 hours before her first nap, and 4 hours before a second one. I was rather using this as a reference than a clock, we never established a routine based on a clock.
Unfortunately, things didn't improve as she got older, she still wakes at different times, however she keeps a rythm for a few days, or a couple of weeks and then changes it again. It is not easy to plan around it but eventually I relaxed and don't worry about this too much. She is also now dropping her nap and things are again upside down. We have bedtime starting at 8 pm on days without nap and at 10 pm on days with a nap.
To answer a first part of your question... This might be a growth spurt as your little one is 3 months old, this is a possibility, as well as the fact he wakes up at different times of the night. Sometimes, filling your baby's tummy during a day won't stop him from nighwakings :cry: . Sometimes, and this is what I think might be going on, these are wakings caused by developmental changes. Is he learning some new skills? Rolling over? This may be the reason too for wakings. Also, is he hungry when he wakes up, if yes, by all means do feed him. At this age they grow a lot and some of this angel babies who slept through start waking again, also because during a day they are too busy to eat properly...