You'd have to have a doctor see your son. And the pediatrician might refer you to a specialist. Whether or not it's autism or something else, getting speech therapy is very helpful.
Throwing tantrums, screaming and yelling, is common for 2 and 3 year olds. The reason behind the tantrums is important to figure out. With my daughter her tantrums were set off because of a few reasons. Sometimes it is/was just your typical I want my way tantrum that all 2 and 3 year olds have. Sometimes it was sensory overload -- she didn't want to be touched or she was overstimulated at the store by too much noise, light, or sound. Sometimes her tantrums were set off because she has a lot of routines and rituals that have to be done a certain way and if you didn't stick to routine of how something was done, she would have a tantrum. Sometimes her tantrums are because she can't speak well enough to share how she's feeling or what she wants. Sometimes she has emotions she can't express. We use pictures with emotion words. They are harder to express with kids with language delays.
Google autism and see what the symptoms are. Your son may have another issue or just have speech delay issues. Or he may have some sort of autistic spectrum disorder or a mild form of one of them. I have a sister who just had some serious language processing disorder issues (she does not have autism) and I remember she was very frustrated growing up until she started getting speech and language therapy. She started speech therapy when she was 4 1/2. But by the time she was in 5th grade you would never have known she had any language problems and got straight As in high school and college.
The only way to know for sure is for your son to be assessed. Those on the autistic spectrum have to have difficulties in three main areas; these are (a) speech. They must have delayed or disordered speech, problems understanding the meaning of words, difficulties following instructions, problems with expressive or receptive speech; (b) social communication. They must have difficulties with social interaction/play with their peer group. This may vary from being totally uninterested in other children, attempting to play but appearing to know how to do it, or being very controlling or overbearing with other children; (c) difficulties around change/transitions. This may mean problems with changes in routine, having to start or stop doing something, rigid behaviours, rituals, flapping/spinning/toe walking etc, lack of imagination/fexibility.
There are also usually problems with sensory integration with senses being over or under sensitive. Google Sensory Integration Dysfunction to see if that sounds relevent to your son. The fact that he speaks slowly and quietly may indicate he has sensitive hearing.
But you are right to be concerned and that you should have his speech and communication assessed by a Speech and Language Therapist. Raise your concerns with the paediatrician and ask for a referal to a speech therapist.